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The sediments of streams and rivers partly preserve the records of the activities that surround them. In natural areas, mineral sediments are deposited and organic plant material is carried by rainfall. If in urban or densely cultivated areas, the records are complemented by other organic materials, and chemicals and solid particles from human activities. Studying sediment profiles of small watercourses throughout their hydrological cycle allows us to observe oscillations in sediment inputs and correlate them with the surrounding uses. This makes it possible to observe influences on erosion processes in areas of exposed soil due to agriculture, on the reduction of water flow in primary channels due to soil sealing and on changes in the solid content of sediments due to the incorporation of anthropogenic materials, like microplastics. The methodological procedures presented in this chapter and used in two case studies carried out the obtention of sediment profiles ranging from 12 to 71 cm in length, enabling in-depth analysis of the content of anthropogenic particles. In the urban basin studied, we found up to 5160 part./kg of microplastics, and in the rural basin, there were only a few sparse fragments, highlighting urban waste and activities as the main source of these materials.
Federal University of São Carlos (UFSCar), Department of Civil Engineering, Program in Urban Engineering (PPGEU), São Carlos, Brazil
Daniele Toyama
Urban Engineering, Program in Urban Engineering (PPGEU / UFSCar), São Carlos, Brazil
Clara Bianchi Bahia
Federal University of São Carlos (UFSCar), São Carlos, Brazil
*Address all correspondence to: denisebm@ufscar.br
1. Introduction
In order to assess the state of integrity of soils, waters and sediments in urban water bodies, it is necessary to characterise the quality of these elements of the physical environment. Many of the interactions between elements occur through water flows from springs and streams that drain urban and rural catchments.
The influence of human beings as modifying agents of the physical environment has long been pointed out. The extent of these modifications and the way they affect the physical and chemical properties of soils, sediments and waters depends on the type of anthropogenic action and the intensity of the alteration caused. The diversity of chemical products and materials has never been greater than it is today [1].
Water resources and their quality are closely related to the characteristics of the geoenvironment (geological formations, soils, surface and underground water bodies, gases and organisms), which give them geogenic signatures; anthropogenic activities, through modifications to geological, physical, chemical and biochemical processes, modify these signatures, incorporating elements that make it possible to identify them [2].
Rivers are the main carriers of sediment loads. Water and wind carry the soil particles that break off to the watercourses, which transport them to the lower reaches. Human action on the vegetation cover, exposing the soil and causing rivers to silt up, can aggravate the natural surface processes. Changes in soil cover allow more rainwater to run off the surface and carry particles of various natural and artificial products into watercourses, increasing sedimentation and changing their compositional characteristics [3].
The study of sediment in watercourses and its composition provides an assessment of the natural components originating from the weathering and erosion of the surrounding rocks and soils, as well as materials originating from human industrial, urban and rural activities upstream, such as plastic, metals, wood, paper, cardboard, bricks and other construction waste that can be incorporated into river sediment. The composition reflects greater or lesser anthropisation; one of the indicators is the presence of plastics (macro or micro), whose dispersion and effects on terrestrial aquatic environments are still poorly studied. Much of the plastic produced is a source of pollution for the geoenvironment and in terrestrial water bodies; it accumulates in places with low water flow velocity, such as lakes, floodplains and meanders [4, 5, 6].
Farming activities are also a major cause of environmental change, interfering with water dynamics as they alter surface geological materials through the revolving of materials excavated, turned over and landfilled, modifying the natural structure, destroying the layer of organic matter and allowing the leaching of materials [7, 8].
These surface alterations have an impact on watercourses and transported sediment, leaving a record of variations in composition and volume in the deposits [9]. In addition, this process of sedimentary deposit formation can change over time due to variations in water flows, influencing the records found [10].
The content and characteristics of the sediment deposited can indicate an input of sediment greater than the transport capacity of the water flow (siltation), the flow of organic matter transported by torrents or the flow of anthropogenic materials or contaminants [11].
Another effect of anthropogenic alterations is that, during rainfall, a greater flow of water reaches the channel, with less infiltration. This suddenly concentrated flow generates marginal erosion and the consequent loss of riparian vegetation. Legally protected, riparian vegetation, when denser and intact, has the capacity to retain part of the flow of sediment and other materials that can reach the watercourse, as well as retain erosion processes on the banks of watercourses.
Evidence of degradation of the physical environment makes it possible to assess the health of the water environment for aquatic fauna, for example. Moreover, they can guide the environmental recovery of the areas drained by the river basin.
In the history of humankind, the Neolithic Revolution represents a milestone in the development of the species and its capacity as modifiers of the physical environment. Previously, natural agents such as volcanic processes, erosion, landslides, weathering and the transport of materials were responsible for remodelling the surface and creating new deposits. After the Neolithic Revolution, there were several technological revolutions, and now humans, as agents modifying the environment, carry out excavations and earthworks, build cities, extract minerals and produce solid waste. It is important to emphasise the intensity of human actions on Earth, especially in comparison with the planet’s lifespan.
As pointed out by [12], human activities in the 21st century move far more sediment per year than all the rivers on Earth, as well as convert half of all habitable land to agriculture. Moreover, rivers, the source of water necessary for life, are turned degraded, polluted and modified.
The human population, through its technology, is capable of irreversible negative changes and impacts. In this sense, the Anthropocene Working Group (AWG) studies whether human impacts can be so significant as to indicate a new geological epoch [13, 14]. Regardless of these chronostratigraphic definitions, in this post-World War II period, the Great Acceleration of population growth, industrialisation and use of mineral and energy resources in the middle of the 20th century, such as the extraction and processing of oil, producing fossil fuels and other derivatives, generated new persistent materials, among them synthetic polymers [15].
Plastics and their incorporation into our daily lives are well known. Their effects on the environment are still being studied.
Disposable plastic appeared in 1909 because of US legislation banning the use of communal cups on trains in order to prevent the spread of disease; in 1938, polyamide (fibres that make up fabrics) was invented, introducing plastic into the fashion industry. In the 1950s, fabrics made from polyester took over the market because they were cheap, were easy to wash and did not require ironing. Between 1970 and 1980, plastic began to be used in the manufacture of children’s toys, spacecraft components and objects related to music and photography. In the 1990s, plastic was used in the automotive industry because it was a lightweight material, increasing the fuel efficiency of vehicles. In the 2000s, on the other hand, the call for environmental protection increased and the issue of recovering and recycling plastics gained attention [16].
In the drinks market, the first tests with plastic packaging took place in 1970 by Coca-Cola and went into commercial production in 1976 by Amoco for Pepsi Cola [17].
In Brazil, the use of plastic bags began in 1980, due to the rising cost of paper [18].
Of all the plastic produced in the world in 2015, 2.5 x 109 tonnes (30.12%) are in use, 0.6 x 109 tonnes (7.22%) were recycled, 0.8 x 109 tonnes (9.63%) were incinerated and the remaining 4.9 x 109 tonnes (59.03%) were disposed of in open dumps and landfills and dispersed in inappropriate places [5]. Much of this material will accumulate and sediment in water bodies.
Given its persistence in the environment, plastic is one of the most important constituents of future technofossils, since it is widely exploited by today’s industry, is present on a large scale in the daily lives of the world’s population [19] and occurs in various sedimentation environments.
Plastic in the environment receives a classification according to its size: macroplastics are those larger than 5 mm, microplastics are smaller than 5 mm [20] and nanoplastics are tens of nanometres or less [5]. Macroplastics are waste that is visible to the naked eye, such as bags, bottles, toys, fishing nets and packaging. Microplastics are not easily visible to the naked eye, being microspheres, pellets and secondary fragments derived from macroplastics and fabric fibres and according to [5] microplastics have a considerable capacity to cause biological damage. The diffusion of nanoplastics possibly occurs to the same extent as the previous ones, but due to the lack of methodology for their detection, they are little studied.
Sediments are a result of hydrosedimentological dynamics and their anthropisation have relation to these characteristics, but also due to the shape and complexity of the different land uses in the surrounding area [21, 22, 23].
In order to understand the diffusion of non-natural particles, our research group is trying to assess the extent to which the sediments are impacted, whether they are composed of anthropogenic materials, whether they are little anthropised or whether they indicate alterations resulting from the environment.
The objectives of this chapter are:
to present the methodology and procedures developed and adopted by the group, seeking to analyse anthropogenic changes and their recording in depth, which highlights changes in deposits over time;
to present and discuss the results of two different applications.
To this purpose, we structured the text as follows: topic 2 describing the methodology and methods of analysis, topic 3 applying it to the determination of microplastics in sediments from urban and rural watercourses and topic 4 applying it to the identification of anthropisation of watercourses in rural areas, seeking to evaluate the different types of results with its application.
We end with a discussion of the results, comparison with other studies and conclusions.
The methodology for collecting sediment profiles and analysing composition and the presence of anthropogenic materials was developed looking for in-depth data, as these are still incipient. It was applied in two locations: first in an urban basin [24] and then in a rural basin [25], the results and specific aspects of which will be presented in sections 3 and 4.
We developed a corer-type sampler and used to collect the sediment profile, which tipe is indicate in studies that aim to verify changes on a temporal scale, since we can observe the successive sediment layers. The sampler consists of a two-inch, 1 m-long geomechanical PVC tube with an internal plunger for suction, working in a similar way to a syringe [26].
As these are shallow bodies of water, sampling takes place inside the channel by driving the sampler into the bed sediment while lifting the plunger, allowing the sample to enter. The sampler is then removed and the sample extracted by pushing the plunger.
In general, samples are taken in two separate collections over the course of a hydrological year in order to observe changes between periods of drought and periods of greater rainfall intensity, which are characteristic of the climate in the southeastern region of Brazil. In the case of climatic features with a different rainfall regime, collections during the year should be adapted.
The sample profiles collected are divided every 10 cm or when different layers occur (textural, compositional or colour variations) and stored.
The sub-samples are dried at room temperature and separated into particle size fractions (>4.75 mm, 4.75 to 1.18 mm and 1.18 mm to 75 μm and < 75 μm) by sieving using a sieve shaker. After sieving, the fractions are weighed and stored.
The particle size fractions referring to pebbles, gravel and other materials >1.18 mm are sorted with the naked eye or using a hand magnifier and tweezers. Anthropogenic fragments found are identified, separated, photographed and stored.
The fraction corresponding to sands between 1.18 mm and 75 μm is quartered using a metal spatula and glass base, prepared and analysed under a stereomicroscope. A quarter of the volume is separated for analysis and a third of the remaining material is kept for replication.
In an attempt to define the best preparation method, we carried out a comparative analysis of samples of this fraction [24] without degradation of organic matter (OM) and with degradation of organic matter. Degradation was chosen because it makes it easier to see the natural material compared to the artificial one, reduces analysis time and minimises possible errors arising from the similarity between plastic fibres and roots and other smaller fragments of organic matter.
The degradation of OM is carried out by adding 30% hydrogen peroxide (no filtering was carried out) to the sediment in beakers or porcelain crucibles [27, 28], using a sufficient volume to cover the sample, which is stirred with a glass rod and then covered to avoid contamination. After the reaction ceases, the samples are dried using a sand bath. Once drying is complete, H2O2 is added again, waiting for oxidation to finish and drying to take place.
At the end of the degradation process, the samples are analysed under a stereomicroscope, taking note of any unnatural particles present, recording them and identifying them where possible.
In the 2 studies presented below, due to their peculiarities, the materials were counted in different ways.
The <75 μm fraction can be sent for chemical analyses, which will not be presented in this chapter.
The presence of plastics in the sediments was the focus of the methodology in this river basin in the interior of Brazil.
The aim of the study was to identify the occurrence of the artificialisation of river sediment and the deposition of anthropogenic material on the bed of water bodies in a river basin, correlating them with the characteristics of urban and rural use of the surrounding area.
The Água Branca Stream Basin drains a large part of the urban area of Itirapina, a municipality located in the interior of the state of São Paulo, Brazil, with an area of 564.603 km2 and 16,148 inhabitants [29].
In this study, we selected sample points (shown in Figure 1) in streams located in areas of greater and lesser urbanisation in order to verify the sedimentation patterns of artificially produced materials.
Figure 1.
Description of the sediment collection points. Source: Author (2019).
The sampling campaigns took place in November 2018 (spring) and May 2019 (autumn). The first campaign occurred after a period of drought from April to July, followed by rainfall of approximately 50 mm until November. The second followed a period of heavier rainfall, reaching 180 mm in February. In May 2019, rainfall halved compared to the previous month.
We also observed the accumulation of man-made materials on the banks or in the bed of the stream. In these cases, we took photographs and collected specimens of interest.
This text will focus on the macro and micro scales of anthropogenic fragments.
The samples collected from the sediment profiles underwent the separation and sorting procedure presented in item 2. For more details on the specific procedures, read [24].
The material retained on the 4.75-mm and 1.18-mm sieves and observed with the naked eye, when there was evidence of plastic material, underwent a heat resistance test that allows plastic, organic matter and mineral grain identification. The description of this procedure is in [24].
The material in the fraction corresponding to sands from 1.18 mm to 75 μm had all the anthropogenic particles separated, photographed, identified (where possible), quantified and statistically evaluated [24].
Plastic, the most common artificial material today, is also present in the air. In this study, we considered the possibility of sample contamination throughout the sorting and sample preparation stage. Therefore, the samples from point P4 (Limoeiro Stream) were defined as blanks for this study. The fibres and other fragments observed at this point could be the effects of contamination and we disregarded them from the analyses, extrapolating to the other points.
Considering the geological substrate of the basin, composed of sandy sedimentary rocks, and the granulometric analysis, the sandy matrix sediments, with little silt and clay, correspond to what was expected. There is a predominance of quartz grains, some opaque minerals (some ferrous with magnetic attraction) and micas. We can find organic material incorporated into the sediment and artificial components such as plastic.
The main anthropogenic material observed was plastic (macro and microplastic). The economy of the study area have a not significant impact by industrial production, so the uses of the basin are predominantly urban (housing) and commercial (sale of finished products and provision of services); the artificial materials found in the samples are a reflection of this occupation. The following sections present the results and discussion of each point studied.
We observed the deposition of materials of artificial origin in the bed of water bodies at some points. The following subsections detail the points where we observed macroscopic traces of sediment artificialisation.
In the bed of the unnamed stream, in the urban area (P1), it is possible to see the deposition of artificial waste such as plastic and cardboard.
In the Água Branca Stream - urban area (P2), the collection occurred in the canalised section of the stream, where we found artificial material such as roof tiles, fragments of bricks, shoes and plastics deposited. We observed the presence of fish and aquatic macro invertebrates.
In the Tibiriçá Reservoir (P6), a place of transition from a lotic to a lentic environment, all the drainage from the upstream basin contributes to the composition of the sediment. The margin of the reservoir has an accumulation of artificial materials and in addition to the sediment pro-files we collected these deposited objects for characterisation.
Figure 2 shows some of these objects. The oldest container found dates back to 1993. This demonstrates the reservoir’s capacity to retain material from the drainage network. All the specimens collected received solar radiation for years. All the items collected are perfectly preserved and the degradation observed in some items is due to mechanical abrasion (e.g. Axe deodorant packaging). The most recent packaging collected was dated 2015.
Figure 2.
Examples of objects collected at Tibiriçá Reservoir deposited within the sediment. Source: Author (2019).
Although some of the material is undated, it is possible to infer its antiquity considering that it is packaging for products that are not in commercial circulation. The observations made show that artificially altered deposits occur mainly in environments with more intense sedimentation.
The sediment profiles collected ranged from 16 to 71 cm in length (longer in P6) and was possible divide them in 2 to 4 sub-samples.
Analysis of the sediment profiles showed that the finer fractions are the ones that make it possible to see the greatest compositional variability.
In the macroscopic analysis we observed few fragments, consisting of microplastics, plant fibres and glass, with the exception of point P6, which showed a greater quantity of anthropogenic fragments at different sample depths. At point P5, in contrast to the samples from the other points where sand predominates, we observed a different sediment composition, with material similar to sawdust used to cover vegetable beds (organic matter).
In addition, we found sticks and leaves from the riparian forest that exists in this stretch. We observed organic matter (fragments of leaves, sticks, algae, macro invertebrate cocoons, seed shells) in the surface layer of point P4, while the deeper layers were mostly composed of sand. At this point, we did not observe the presence of artificial materials as expected.
Microscopic analysis revealed many fragments. Table 1 shows the quantity of plastic fragments, plastic fibres and other materials (paper or glass) observed in the profiles studied (material between 1.18 mm and 75 μm in size).
Fragments
Fibres
Other
Total
2018
2019
2018
2019
2018
2019
2018
2019
P1.1
part./100 g
14
9
19
76
0
0
34
85
part./kg
140
90
190
760
0
0
340
850
P1.2
part./100 g
0
49
22
130
0
0
22
179
part./kg
0
490
220
1300
0
0
220
1790
P2.1
part./100 g
20
40
72
29
0
0
92
69
part./kg
200
400
720
290
0
0
920
690
P2.2
part./100 g
8
8
65
40
4
0
77
48
part./kg
80
80
650
400
40
0
770
480
P2.3
part./100 g
11
12
2
0
0
0
13
12
part./kg
110
120
20
0
0
0
130
120
P3.1
part./100 g
2
1
13
16
0
0
15
17
part./kg
20
10
130
160
0
0
150
170
P3.2
part./100 g
0
1
2
10
0
0
2
12
part./kg
0
10
20
100
0
0
20
120
P3.3
part./100 g
0
3
0
0
0
0
0
3
part./kg
0
30
0
0
0
0
0
30
P3.4
part./100 g
0
—
20
—
0
—
20
—
part./kg
0
—
200
—
0
—
200
—
P3.5
part./100 g
0
—
4
—
0
—
4
—
part./kg
0
—
40
—
0
—
40
—
P4.1
part./100 g
0
0
0
0
0
0
0
0
part./kg
0
0
0
0
0
0
0
0
P4.2
part./100 g
0
0
0
0
0
0
0
0
part./kg
0
0
0
0
0
0
0
0
P4.3
part./100 g
0
0
1
0
0
0
1
0
part./kg
0
0
10
0
0
0
10
0
P5.1
part./100 g
30
13
6
10
0
0
36
23
part./kg
300
130
60
100
0
0
360
230
P5.2
part./100 g
13
5
32
13
0
0
45
18
part./kg
130
50
320
130
0
0
450
180
P5.3
part./100 g
8
17
12
0
1
0
22
17
part./kg
80
170
120
0
10
0
220
170
P6.1
part./100 g
86
17
430
26
0
0
516
43
part./kg
860
170
4300
260
0
0
5160
430
P6.2
part./100 g
9
3
82
11
0
0
91
14
part./kg
90
30
820
110
0
0
910
140
P6.3
part./100 g
5
—
31
—
0
—
36
—
part./kg
50
—
310
—
0
—
360
—
P6.4
part./100 g
12
—
42
—
0
—
55
—
part./kg
120
—
420
—
0
—
550
—
Table 1.
Average number of artificial micro-materials observed in the sediment in the study area (sorting with a stereomicroscope, referring to grain sizes between 75 μm and 1.18 mm). Where: -, non-existent layer and 0, no fragments.
Source: Author (2020).
Figure 3 shows some examples of the fragments recorded in 2018 and 2019.
Figure 3.
Fragments of artificial materials observed in the 2018 samples in the sediment of the bodies of water in the Água Branca Stream basin. Scale: 1 mm. Source: Author (2020).
A detailed analysis of the results follows in [24].
The results indicate that the Água Branca stream basin is undergoing a process of artificialisation of the sediment of urban water bodies, with microplastics being the most significant materials incorporated into the sediment profile.
The sedimentation and accumulation of materials visible to the naked eye (macro fragments) such as cardboard, plastics and the remains of construction materials can be seen in the stream beds.
The Tibiriçá Reservoir - P6 (a lentic environment with a slower water flow) has the greatest accumulation of micro and macroplastics, as shown in Figure 3. This site receives all the drainage from the urban area of Itirapina, which is part of the Água Branca Stream basin, and seems to contain the macroplastics. It was possible to collect packaging dating back to 1993, showing the degradation caused by poor solid waste management.
Of the material observed, the lowest concentration is in the deepest layer of the sediment, indicating greater removal of light materials by the water or greater recent input of anthropogenic materials.
In the study, we observed that a higher percentage of artificial materials occurs in the November 2018 collection compared to May 2019. It may be related to the intense rainy season prior to the last collection, which may have carried a greater contribution of mineral sediments and carried away the fragments of microplastics, which are the main materials found.
We concluded that the type and intensity of land use influences the amount of microplastics. Considering the watercourses (lotic environments) in the tributary of the Água Branca Stream in an urban area with a lower density of occupation and surrounding grass vegetation (P1), we found a lower amount than at the point in the urban centre (P2), surrounded by commercial and residential use and without riparian vegetation. We observed the highest concentration of artificial materials at this point. The point located in a rural area had less artificial material than the other two.
This highlights the need for intervention to prevent this artificialisation from intensifying as the city grows. Aquatic invertebrates and fish consume microplastics, and in turn, they serve as food for humans (knowledge about the deleterious effects on humans is still limited). An action to clean the reservoir and remove large plastics would be important to prevent them from degrading and generating new microplastics in the future.
The aim of this study was to identify the environmental quality and geoenvironmental changes of a watershed between a rural area and an area of environmental protection, by means of a set of environmental data and verification of the influence of land use on watercourses through deposited sediments.
The Barrinha Stream basin, with an estimated area of 7.7 km2, in the district of Cachoeira de Emas, municipality of Pirassununga located in the interior of São Paulo state, Brazil, is a micro-watershed that is under the influence of surrounding uses (Figure 4).
Figure 4.
Micro-basin of the Barrinha stream with the delimitation of the CEPTA area, study points and sample collection. Sources: [30, 31].
Although much of it is within the area of the National Centre for Research and Conservation of Continental Aquatic Biodiversity - CEPTA - ICMBio, there are some springs occupied by various agricultural and urban uses, which are impacting soil degradation, sediment input into the stream, natural vegetation and, consequently, local aquatic life. Although it is not a protected area, the farm area has fragments of cerrado (savannah), cerradão (forested savannah) and riparian vegetation that are well preserved and where environmental education activities occurs.
The Barrinha Stream is a second order watercourse and was originally 3180 m long. However, after the installation of five dams, embankments and the construction of tanks, around 27% (approximately 877 m) of the original length was affected [31]. The institution’s fishing ponds uses the water.
The collection methodology used a corer sampler to verify the composition and characteristics of the sediments, identifying possible points of sediment accumulation and siltation related to the degradation of the basin’s soil and its variability in depth, which would be related to the periods of greater and lesser water flow in the channels.
The sediments of the Barrinha stream were collected in two periods, one in the autumn of 2022 (May) after the rainy season and the second in the middle of the rainy season in the summer of 2023 (March).
The samples were collected at 4 points (P166, P173, P174, P175), which run from the floodplain of the spring to near the mouth of the stream (Figure 5).
Figure 5.
Sediment collection points, UTM WGS 84 coordinates (m). Description of the points in May 2022 and March 2023. Source: Authors, 2022.
As a result of this study, we observed great variability in water flows, with some stretches already characterised as intermittent.
The area of the course’s main source, in a floodplain, is dry almost all year round. The influence of the surrounding sugar cane plantations is evident. It was not possible to collect recent sediment at this site.
In May 2022, the Barrinha Stream had little water flow and some of the points studied were dry or with little water. In March 2023, at the end of a period of intense rainfall, the stream had a greater quantity of water, but in some places, such as P174, there was already a significant accumulation of organic matter, indicating that the transport of mineral materials was not happening with such intensity and there was already a decrease in water flow, although the tributary that flows into this point had a good water flow. P175, at the mouth of the Barrinha Stream on the Mogi Guaçu River, had a rise in level of approximately 1 m, influenced by the flooding of the latter, and it was not possible to collect profile 2.
The samples collected measured between 12 and 31 cm in length. We separated the profiles collected (Figure 6) into 1 to 4 sub-samples samples by homogeneous sections (colour, texture, fraction), that we sent to the laboratory for analysis.
Figure 6.
Examples of the profiles collected in the area. Source: Photographs by the authors (2022).
The fraction separation and treatment procedures were the same as those described in item 2, with some modifications because there were points with a large accumulation of macroscopic organic matter (branches and leaves, for example) and also because the sediment was finer and more aggregated.
The samples were left to dry at room temperature and, for the silt-clay samples that were more difficult to dry, we used an open oven. The use of a closed oven is not recommended because there is a risk of burning other materials present in the sample, such as anthropogenic materials.
After drying, the samples were first analysed visually, looking at the content of the organic matter fragments and their size. Then we weighed the samples and the visible organic matter (e.g. twigs, seeds, leaves, small insects) separated.
In this study, there were many samples with a large amount of OM and we used degradation. The method promotes the removal of organic colloids and the dispersion of clay, facilitating the granulometric separation of the fractions [32].
We analysed 16 samples from Barrinha Stream in May 2022 and 12 samples in March 2023 (Table 2).
May/2022
March/2023
Point
Total (cm)
Sample
Length (cm)
% OM
Total (cm)
Sample
Length (cm)
% OM
p. 166
31
1
17
25.5
1
12
4.82
2
5
2
10.5
5.64
3
5
3
3
7.79
4
4
2.5
p. 173
No profile taken (=40)
1
9.17
23
1
3
2
5.3
2
10
3
2.33
3
7
4
3
8.84
p. 174 (perfil 1)
12
1
8
14.7
22
1
6
2
4
3.1
2
16
p. 174 (perfil 2)
18
1
6.5
22
1
17.5
2
9.5
2
4.5
3
3
p. 175 (perfil 1)
21.5
1
6.5
1.3
15
1
15
2
13
p. 175 (perfil 2)
15
1
7.5
No collection due to excess water
2
7.5
Table 2.
Measurement of the samples collected in May 2022 and March 2023 and % MO of the samples that underwent degradation with H2O2.
Profile 1 of P175, which had been subdivided into three samples in the first collection, showed only one sample of homogeneous sediment in the second collection, indicating greater deposition of mineral materials, compatible with the input during the rainy season.
Analysis of the sediment samples showed that in the period without rainfall (May 2022) there was more accumulation of OM (> %), in more subsamples of the sand fraction, compatible with the period of lower water flow.
In the May 2022 collection, Am1 from P174 - profile 1 had the most organic matter, accounting for 14.7% of its total weight. Am1 from P175 - profile 1 was the sample with the lowest percentage of organic matter of its total weight, with only 1.3%.
However, in the 2023 collection, only four samples underwent the procedure. And of these four, the sample with the highest percentage of organic matter is Am 3 from P173, indicating a large input of sediment coming with the water flow and deposited on the previously dry site with a large amount of MO deposited, which corroborates the result found.
The granulometric separation (Table 3) showed that sandy sediments predominate (fraction between 1.18 and 0.75 mm).
Point
Sample (Am)
Total sample weight (g)
Fraction weight > 4.75 mm (g)
Fraction weight between 4.75 and 1.18 mm (g)
Fraction weight between 1.18 and 0.75 mm (g)
Fraction weight < 0.75 mm (g)
May 2022
166
1
29.93
0
1.44
27.81
0.53
2
30.35
0
3.85
25.87
0.61
3
31.04
0
0.61
29.57
0.65
4
29.14
0
0.27
27.83
0.54
173
1
21.81
0
0.16
15.80
5.85
2
26.81
0
<0.001
14.55
11.91
3
28.99
0
<0.001
25.46
3.46
174 (prof 1)
1
6.94
0
<0.001
4.44
2.42
2
35.74
0
0.45
32.02
3.48
174 (prof 2)
1
30.40
0
<0.001
29.70
0.35
2
30.57
0
0.66
29.54
0.28
3
30.84
0
0.87
29.25
0.33
175 (prof 1)
1
31.36
0.69
0.45
32.02
3.48
2
171
96.04
2.44
64.98
7.37
175 (prof 2)
1
37.01
8.13
1.50
25.30
2.23
2
196
104.83
15.29
63.49
3.09
March 2023
166
1
29.21
0
0.009
27.71
1.35
2
28.93
0.87
2.23
23.57
2.09
3
28.29
1.6
2.93
20.40
2.52
173
1
18.55
4.78
7.4
5.5
0.89
2
30.48
0
2.2
25.31
3.2
3
27.75
0
0.009
23.3
4.1
4
30.28
0
0.14
26.68
2.93
174 (prof 1)
1
31.29
3.35
8.36
17.57
0.66
2
30.18
0.26
2.12
25.5
1.8
174 (prof 2)
1
30.59
0
0.62
29.76
0.001
2
30.51
0
1.28
28.28
0.85
175 (prof 1)
1
30.39
0
0.89
24.82
4.05
Table 3.
Weight of the samples collected and their respective fractions.
The samples from P175, profile 1/Am2/2022 and profile 2/Am2/2022 had fragments of basaltic and sandstone rocks and a greater weight of the >4.75 mm fraction.
Stereomicroscope analyses revealed that there were not many fragments of anthropogenic materials.
The May/2022 samples had the same basic composition: quartz with some iron oxide concretions. Samples P165 - Am1 (floodplain area) and P166 - Am4 had a large amount of OM (roots, branches, seeds and bark) in all fractions. Sample P166 - Am3 had a fibre that appeared to be fabric and sample P175 (profile 1) - Am 2 had a fragment of foam.
In the March/2023 samples, the composition remained the same. However, we observed more rounded grains of quartz, indicating a possible different source of the material. Samples P173 - Am2, P174 (profile 1) - Am1 and P174 (profile 1) - Am2 contained a large amount of OM, such as seeds or twigs, in all their fractions. Sample P174 (profile 1) - Am1 had a fragment that looked like cardboard. Sample P174 (profile 2) - Am1 had a plastic fragment (Figure 7).
Figure 7.
Photographs of items highlighted in the microscopic analysis. Source: Author (2023).
The presence of quartz grains in all the samples reiterates the perception that the micro-basin has mainly sandy-textured soil.
The use of the surrounding land (crops, mining and dams) has negatively affected the environmental quality of the watershed. Temporary crops such as sugar cane mostly occupy the basin. The areas with anthropogenic influence reduce the flow of surface water, as in the reduced floodplain due to nearby temporary crops, and generate an increase in sediment in the watercourses. The preservation of forest vegetation is greater within CEPTA’s boundaries, favouring the availability of water and the balance of the streams, such as the spring that flows into P174. We also observed eroded areas and exposed soil used for dumping waste, which are source areas for the sediment that reaches the stream.
In conclusion, it is clear that the use of the area around the Barrinha Stream has significantly affected its watercourse. We found many points with sediment accumulation, raising the concern of possible silting of the water body, combined with the low water flow, which prevents sediment transport. We found traces of materials of human origin in sediment samples, as well as the greater degradation of water bodies where there is construction in the surroundings. The floodplain area is almost permanently devoid of water accumulation, and organic soil has shown that there has been a reduction in its perimeter, influencing the flow of the Barrinha Stream, which is intermittent at various points where there was a continuous flow observed in previous research in 1994 [33].
The area of forest on CEPTA’s perimeter and its effect on the perenniality of the watercourses highlight its importance for preserving native vegetation in the basin, in contrast to the surrounding areas where cultivated land predominates.
It is necessary to invest in measures to protect and conserve the watercourses in order to minimise the negative impacts of the use of the surroundings, especially the springs.
The formation of river sediments with anthropogenic alteration occurs when artificial materials are incorporated into the riverbed. Plastics are the main solid waste generated in urban centres, so they are the main waste incorporated into sediments.
There is a great deal of media coverage of the harmful effects of plastics on the aquatic environment, degrading not only the quality of this resource but also the biota. Despite being a major current environmental problem, research into the impacts of this material is also recent, especially if we consider microplastics (particles smaller than 5 mm) [34].
According to the survey carried out by [35], benthic fauna can consume microplastic incorporated into river sediment depending on the organisms’ feeding mode. In Serra Talhada, Pernambuco, Brazil, [36] observed plastic residues in the stomach contents of 83 per cent of the fish collected. These researchers state that their study suggests that the biota is vulnerable to the microplastics present in freshwater and that they are associated with areas with more intense urbanisation, also highlighting that the poorest community feeds on these fish.
With regard to the harmful effects of microplastics in drinking water, the World Health Organisation (WHO) [37] states that the knowledge available to date is limited and represents a low concern for human health. On the other hand, this same lack of conclusive studies is a cause for concern, because it is still unknown how these particles act on our bodies.
The WHO points out that plastics have low toxicity and, because they are insoluble, are unlikely to be absorbed by the gastrointestinal tract. However, it also points out that particle size can influence the absorption of toxicity, with smaller particles posing a greater risk. He also points out that additives and monomers (molecules made up of a single segment) can become bioavailable in the gastrointestinal tract [37]. The human body exposes itself to microplastics through ingesting food or water containing microplastics, inhaling microplastics in the air or dermal contact through textiles or air [38].
As pointed by [39], each person ingests 39,000 to 52,000 microplastic particles per year, depending on the age and gender of the individual. If we consider inhalation, this value varies between 74,000 and 121,000 particles per person. Also according to these authors, if we consider the recommended water intake using only bottled water, a consumption of 90,000 microplastic particles occurs, while if only tap water is consumed there are 4000 particles (research carried out considering a North American diet).
According to [38], the increase in the occurrence of neurodegenerative diseases, immunological disorders and cancer may be related to increased exposure to environmental contaminants, including microplastics. Therefore, knowing the distribution pattern of these materials and quantifying them is of the utmost importance to subsidise future studies related to research into the harmful effects on humans.
From a geological point of view, studies suggest that the artificialisation of sediment can change the patterns of sediment erosion, transport and deposition. An initial experiment carried out in the laboratory considered different microplastics (types, shapes and sizes) compared to natural sediment. Microplastics with spherical shapes move more quickly compared to natural sediments [40].
The results obtained in the studies are in line with the global trend of increasing concentrations of artificial materials incorporated into river sediments.
The bibliographical research showed the lack of studies carried out in tropical freshwater river environments, especially studies of layer profiles. In this sense, our research helps to understand the behaviour of riverbed sediment anthropisation.
Until now, there are no standardised methods for detecting microplastics in sediments, which makes comparisons difficult.
Table 4 summarises the main research carried out on the subject, relating to sediment collection methodologies and analysis of the results.
Investigate the abundance, distribution and sources of MPs in Tibetan river sediments collected with stainless steel shovel
The abundance of MP in the sediments of urban areas was higher than that in rural areas. But there was no statistical difference in the surface water of urban and rural areas
Estimate MP values in the water column and surface sediments in Florida’s largest estuary (Tampa Bay), including spatial and temporal variations in these values
Found highest concentrations of MP in sediments close to industrial sources. It is impractical to remove the numerous and tiny microplastic particles from the water or sediments
Check for a correlation between local characteristics and the abundance of MPs in sediments of a river in Canada, using a Petite Ponar Grab for sampling
Concentrations of MPs are due to environmental filters, point sources and sediment characteristics
Establish the magnitude of contamination of benthic sediments by MPs and explain the observed patterns in abundance and distribution in rivers in the United Kingdom
The biggest change in MP abundance was due to the presence of a lake, more than to population density. They observed a mechanism of MP fixation in freshwater environments by caddisflies
Investigated sources, fate and seasonal and spatial distribution of MPs in a river basin and estuary in China, investigating water and sediment. Used a grasp bucket for sediment
Areas with high population and gross domestic product presented more MPs in sediment and water, indicating impacts of human activities and economic activities
They studied the sediments upstream and downstream of the French metropolis, with collection of sediment profiles and dating
There is a greater volume of MP downstream and also in more recent layers, but with a decrease in polymers from industrial sources
Table 4.
Summary of the main objectives and results of the most recent research into microplastics (MP) in sediments.
With regard to the sampling methodology and its results, we observed that studies are converging towards obtaining in-depth data, with profile sampling, emphasising the relevance of the methodology proposed in this chapter. The results we obtained are consistent with those obtained in other studies [21, 22, 49, 50].
The degradation of the organic matter in the samples proved to be important in facilitating the visualisation and optical identification of the artificial materials incorporated into the sediment in the two cases studied. In the second case, in an area with a higher content of riparian vegetation, it was crucial to separate the humidified OM from the mineral grains and other fragments.
As [45] states, it is impractical, if not impossible, to remove microplastics from the water column or separate this contamination from sediments and that the best way to reduce the potential risks of this contamination is to control the source of microplastics entering the aquatic system. The environmental legislation aimed at restricting plastics may be responsible for the reduction in some types of plastic found in some studies [10].
There are various methods of sediment collection used to study anthropisation and detection of non-natural particles, such as microplastics, and it is not possible to make a complete comparison of the results found or even of the most correct methodology [23, 50].
In this research, we developed the geomechanical PVC sampler, which fulfilled its functions and proved to be a viable and low-cost tool, but it is necessary to discard from the fragment counts all the possible particles of this material found in the sediments. Other studies have used samplers with transparent PVC liners, with the same problem of the possibility of contamination [10], but the analysis of the volume collected per layer is lost when the aim is to evaluate particles per volume collected. With the sampler used, it was possible to take sediment samples of a significant size (from 16 to 26 cm in the first study and from 12 to 31 cm in the second), within the range of values obtained in other studies [51].
The study of sediment can lead to an understanding of the degradation caused to the aquatic system and the sediment profile can show us the impacts suffered by the water body over time [52]. In the two cases studied, we observed this degradation.
In the Água Branca Stream basin, the urban influence left this record in the microplastic content, and the influence of lentic areas on retention was clear from the macroplastics found and their dating. Although solar radiation and water play the role of degradation, considering the intact materials deposited there since the 1990s, contamination by microplastics will be long-lasting. Considering the maximum values of 5160 part./kg in the 2018 sampling in P6 and comparing it with profile data from different areas from the mainland to the mouth, analysed by [51], these are compatible with some lakes and floodplains, although there are others with much higher levels and this is related to the occupation characteristics.
With regard to the rural area studied, we saw that in the sediments of Barrinha Stream, there are few plastic fragments, but the reduction in water and the large amount of sediment contributed by the replacement of natural vegetation with temporary crops are evident. For this site, studies of physico-chemical parameters may reveal other influences of agricultural activities on sediment quality. It was possible to observe that, even when the volume of anthropogenic fragments is not significant, the sediment analysis records the variations in flow and sediment input that occur over time due to occupation of the surroundings.
The knowledge and impacts of waste in the ocean is widespread, but there is still no good knowledge of these impacts in freshwater environments; likewise, research in this field is also recent, and there are no conclusive studies on the impact of microplastics on the human body, for example.
In the last years, several articles have been published dealing with continental sediments, but there is still no unified methodology and since this is a new field of study, all new approaches are necessary and important. The generation of standardised methodologies and norms happens after many different studies and methods, arriving at a robust state of the art.
The methodological procedures for sediment collection and analysis presented in this chapter and used in the two case studies possibilited in-depth analysis of the content of anthropogenic particles in the sediments, highlighting urban waste and activities as the main source of these materials.
Future studies of sediments must deal with their dating, as carried out by [10] for a more precise assessment of the inputs and removals of microplastics by water during hydrological cycles.
There is a need to expand and disseminate legislation that defines more restrictions on the use of plastics, especially those aimed at controlling disposable utensils.
It is therefore important to emphasise the importance of Environmental Education and scientific dissemination projects on the subject and to bring knowledge to the community, sensitising them to the degradation of aquatic environments and the ingestion of microplastics by invertebrates and fish and the possible impacts on human health. It is also important to emphasise the damage caused to watercourses by changing land uses; the human population grows and loses water sources necessary for its survival.
This study was financed by: the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001; grant The National Council for Scientific and Technological Development (CNPq) PIBIC – UFSCar; grant 2022/01276-9, São Paulo Research Foundation (FAPESP) FAPESP.
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Written By
Denise Balestrero Menezes, Daniele Toyama and Clara Bianchi Bahia
Submitted: 12 January 2024Reviewed: 04 April 2024Published: 15 July 2024
Open access peer-reviewed chapter - ONLINE FIRST
