Contaminated Stream Sediments Research Articles

Machine learning approaches to identify spatial factors and their influential distances for heavy metal contamination in downstream sediment

Contaminated sediments can adversely affect aquatic ecosystems, making the identification and management of pollutant sources extremely important. In this study, we proposed machine learning approaches to reveal sources and their influential distances for heavy metal contamination of downstream sediment. We employed classification models with artificial neural networks (ANN) and random forest (RF), respectively, to predict the heavy metal contamination of stream sediments using upland environmental variables as input features. A comprehensive Korean nationwide monitoring database containing 1546 datasets was used to train and test the models. These datasets encompass the concentrations of eight heavy metals (Ar, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in sediment samples collected from 160 stream sites across the nation from 2014 to 2018. Model's prediction accuracy was evaluated for input feature sets from different influential upland areas defined by different buffer radii and the watershed boundary for each site. Although both ANN and RF models were unsatisfactory in predicting heavy metal quartile classes, RF-classifiers with adaptive synthetic oversampling (ORFC) showed reasonably well-predicted classes of the sediment samples based on the Canada's Sediment Quality Guidelines (accuracy ranged from 0.67 to 0.94). The best influential distance (i.e., buffer radius) was determined for each heavy metal based on the accuracy of ORFC. The results indicated that Cd, Cu and Pb had shorter influential distances (1.5–2.0 km) than the other heavy metals with little difference in accuracy for different influential distances. Feature importance calculation revealed that upland soil contamination was the primary factor for Hg and Ni, while residential areas and roads were significant features associated with Pb and Zn contamination. This approach offers information on major contamination sources and their influential areas to be prioritized for managing contaminated stream sediments.

Large extent of mercury stable isotope fractionation in contaminated stream sediments induced by changes of mercury binding forms

Mercury (Hg) release from contaminated legacy sites is a large contributor to riverine ecosystems and can represent a significant local and regional environmental issue even long after the initial site contamination. Understanding processes of in-stream species transformation is therefore important to assess the fate and bioavailability of the released Hg. In this study, we investigated in-stream Hg transformation processes with analyses of Hg binding forms and Hg stable isotopes. Stream sediments were collected downstream of a former kyanization facility (Black Forest, SW Germany), where highly soluble Hg(II)-chloride (HgCl2) was used as an anti-fouling agent to treat timber. Exfiltration of partly anoxic, contaminated groundwater with Hg concentrations of up to 700 μg L−1 into the adjacent Gutach stream is the main source of Hg to sediments. Total Hg concentrations in the stream bottom sediments (<2 mm) ranged from background values of 6.3 µg kg−1 upstream of the contaminated site to 77 mg kg−1 near the location of exfiltration of contaminated groundwater. A five-step sequential extraction procedure and Hg pyrolytic thermal desorption (PTD) analyses indicated changes in Hg binding forms in the sediments along the flow path towards a higher proportion of organically bound Hg. A large shift towards negative δ202Hg values was observed downstream of the contaminated site (change of ≈2‰) along with a minor offset in mass-independent fractionation. Binary mixing models based on Hg isotope ratios using one industrial and different natural background endmembers were tested to estimate their respective contribution of Hg to the sediments but failed to produce plausible allocations. Based on the observed changes in isotopic composition, total Hg concentrations and Hg binding forms, we propose that the large extent of fractionation observed in downstream sediments is the result of a combination of kinetic isotope effects during sorption, redistribution of Hg within the sediment and the preferential transport of Hg associated with the sediment fine fraction. These results highlight the importance of transformation processes when assessing the sources and fate of Hg in environmental systems and show limitations of using simple mixing models based on Hg stable isotopes.

Sources, speciation and transformation of arsenic in the gold mining impacted Jiehe River, China

Mining-contaminated waters may contain high levels of arsenic (As) and iron (Fe), among various metals and metalloids. The complex behavior of As makes its contamination difficult to remediate. This study aimed to determine the sources, possible association of As and Fe with colloids and their speciation and mobility in the Jiehe River, a stream impacted by gold mining. Particulate (>450 nm), colloidal (7–450 nm), and truely dissolved (<7 nm) forms of As and Fe were determined, and the species of As [As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid] and Fe [Fe(II) and Fe(III)] were both analyzed and modelled using geochemical program Visual MinteQ 3.0. High concentrations of As and Fe were observed in both filtered and particulate forms in most of the water samples. Total As was in the range of 1.0–719 μg L−1 with a median of 140 μg L−1. Total Fe was 0.4–68.2 mg L−1 with a median of 15.0 mg L−1. Arsenic was mainly adsorbed on ferrihydrite, goethite, and hematite in the upstream water samples. In contrast, it was mostly in truely dissolved forms in the water samples at downstream. Visual MinteQ 3.0 modelling results revealed that As adsorbed on, or co-precipitated with, stream sediment can be easily released under the environmental conditions of the downstream reach (11.4–37.5 km). These findings would benefit the environmental management of gold mining impacted Jiehe River, and indicate the need for further quantitative research on As migration facilitated by Fe (hydr)oxide colloids and the release of As from contaminated stream sediments.

Uranium and thorium leachability in contaminated stream sediments from a uranium minesite

The leachability and potential environmental risks of uranium (U) and thorium (Th) in aquifer sediments from a recent uranium minesite of northern Guangdong Province, China were investigated as part of ongoing environmental investigations. Data for the non-mineralogical portion of U, Th and of additional major elements (Mn, Fe, Ca, Mg, Na, Al and K) using a 0.5mol/L HCl partial leach and inductively coupled plasma optical emission spectrometry (ICP-OES) were presented for the contaminated sediments and a background sediment. The contaminated sediments reported leachable contents of U between 22.85 and 2700μg/g and those of Th between 4.800 and 102.1μg/g, which exceed by a few to several hundred times the respective content found in the background. Generally, the leachable U and Th contents in the stream sediments decrease with distance from the potential contamination sources. A special case is the runoff gathering reservoir located around 1km downstream of the U mine-site, representing the most severe metal contamination hotspot within the alpine watershed, where the highest leachable content of U and Th in the inlet sediment was observed. The highest leachability of U (68.6%) and Th (44.8%) was observed in this sediment as well, indicating a high potential of bioaccumulation and bioconcentration of U and Th under changing geochemical conditions. Correlations analysis indicates that the dilute HCl leachable fraction of U and Th bound in the sediments are strongly dependent on anthropogenic inputs from the U mining/milling activities, and Ca salts are the main vectors.

Geochemical comparison of waters and stream sediments close to abandoned Sb-Au and As-Au mining areas, northern Portugal

Waters from abandoned Sb-Au mining areas have higher Sb (up to 2138μgL−1), As (up to 1252μgL−1) and lower Al, Zn, Li, Ni and Co concentrations than those of waters from the As-Au mining area of Banjas, which only contain up to 64μgL−1 As. In general, Sb occurs mainly as SbO3− and As H2AsO4−. In general, waters from old Sb-Au mining areas are contaminated in Sb, As, Al, Fe, Cd, Mn, Ni and NO2−, whereas those from the abandoned As-Au mining area are contaminated in Al, Fe, Mn, Ni, Cd and rarely in NO2−. Waters from the latter area, immediately downstream of mine dumps are also contaminated in As. In stream sediments from Sb-Au and As-Au mining areas, Sb (up to 5488mgkg−1) and As (up to 235mgkg−1) show a similar behaviour and are mainly associated with the residual fraction. In most stream sediments, the As and Sb are not associated with the oxidizable fraction, while Fe is associated with organic matter, indicating that sulphides (mainly arsenopyrite and pyrite) and sulphosalts containing those metalloids and metal are weathered. Arsenic and Sb are mainly associated with clay minerals (chlorite and mica; vermiculite in stream sediments from old Sb-Au mining areas) and probably also with insoluble Sb phases of stream sediments. In the most contaminated stream sediments, metalloids are also associated with Fe phases (hematite and goethite, and also lepidocrocite in stream sediments from Banjas). Moreover, the most contaminated stream sediments correspond to the most contaminated waters, reflecting the limited capacity of stream sediments to retain metals and metalloids.

Soil washing of As-contaminated stream sediments in the vicinity of an abandoned mine in Korea

A soil washing process was applied to remediate arsenic (As)-contaminated stream sediments around an abandoned mine in Goro, Korea. Laboratory scale soil washing experiments for As-contaminated stream sediments were performed under various washing conditions in order to maximize As removal efficiency. Stream sediments were taken from two sites (S1 and S5) along the main stream connected to an abandoned mine. Stream sediments at the two sites were divided into two groups (>or=0.35 and <0.35 mm in diameter), giving four types of sediments, which were thereupon used for soil washing experiments. The results of soil washing experiments involving various pH conditions suggested that As removal efficiency is very high in both strongly acidic and basic solutions (pH 1 and 13), regardless of sediment type. Removal efficiencies for fine sediments from S1 and S5 were >95% after 1 h of washing with 0.2 M citric acid (C(6)H(8)O(7)). When using 0.2 M citric acid mixed with 0.1 M potassium phosphate (KH(2)PO(4)), the As removal efficiency increased to 100%. When recycled washing solution was applied, As removal efficiency was maintained at a level greater than 70%, even after eight recycling events. This suggests that the recycling of washing solution could be successfully applied as a means of decreasing the cost of the washing process. Results from the experiments suggest that soil washing is a potentially useful process for the remediation of As-contaminated stream sediments around abandoned mines.

Antimony and arsenic dispersion in the Macleay River catchment, New South Wales: a study of the environmental geochemical consequences

A baseline geochemical study of stream sediments and waters of the Macleay River catchment in northeastern New South Wales indicates that although most of the catchment is unaffected by anthropogenic or natural inputs of heavy metals and metalloids, the Bakers Creek – trunk Macleay-floodplain system has been strongly affected by mining-derived Sb and As. The dispersion train from the Hillgrove Sb – Au mining area to the Pacific Ocean is over 300 km in length. Ore and mineralised altered rock from Hillgrove contains vein, breccia-hosted and disseminated stibnite, arsenopyrite, pyrite and traces of gold. Historic (pre-1970) mine-waste disposal practices have resulted in high to extreme contamination of stream sediments and waters by Sb and As for ∼50 km downstream, with high Au values in the sediments. In this high-energy fluvial interval, average values of Sb in stream sediment exceed the catchment background (1.1 ppm Sb) by a factor exceeding 200. Similarly, average As values exceed catchment background (7.9 ppm As) by a factor of over 20. Drinking-water guideline values for Sb and As are exceeded by one to three orders of magnitude. Further downstream, stream sediments and floodplain sediments have lower Sb and As contents, although Sb values consistently exceed current interim sediment quality guideline values. Water quality in the trunk Macleay is not strongly affected and drinking-water guideline values for Sb and As are only exceeded locally. Although small volumes of near-neutral mine-water seepages at Hillgrove contain extreme values of dissolved Sb and As, it is likely that much of the stream-water loadings of Sb and As have been liberated from reaction with contaminated stream sediments under near-neutral oxidising conditions. It is demonstrated that Sb and, to a lesser extent As, are bioavailable, with uptake into common riparian vegetation and aquatic alga species. Flood dispersion of contaminated sediment over the Macleay floodplain has formed a layer up to 60 cm thick. In this environment, mobility and bioavailability of Sb and As occur in reducing organic-rich conditions in backswamps, oxidising acidic conditions attending acid sulfate soils and in contemporary pasture and crop growth. Estimates of sediment migration rates and amounts of Sb and As transported in suspension and solution imply that the catchment contamination will be long-term (centuries to millennia) such that environmental effects need to be ascertained and management strategies implemented.

Evaluation of As and Sb Mobility in Contaminated Stream Sediments

Single and sequential extraction procedures were applied to four sediment samples collected from an industrially polluted region of Eastern Slovakia. A sequential extraction procedure (SEP) for sediments recommended by the IRMM (Institute for Reference Materials and Measurements) – was applied and used as a reference extraction method. Single-step extraction (for soils) with 0.05 mol L−1 ethylenediaminetetraacetic acid (EDTA) was slightly modified for this study of sediments. The removal ability of “Na2EDTA extraction” was compared with the SEP recommended by the IRMM. After optimisation, the elements’ contents extracted into Na2EDTA were in good agreement with the sum of the 1st, 2nd, 3rd and 4th step of SEP for As and Sb. Therefore Na2EDTA extraction can serve as a supplementary test to the SEP recommended by the IRMM (under locally tested conditions). Alternatively, optimised extraction of sediments in chelating agents could be applied as an economically interesting and time-saving supplementary test to routinely used SEPs. This paper describes the sample preparation and the analytical results for each extraction step and compares the results with those of total element analyses (performed by an independent method) for As and Sb.

Occurrence of Organochlorine Pesticides in Stream Sediments from an Industrial Area

Contaminated stream sediments are a serious problem because contaminant residues will be persistent for a long time. Organochlorine pesticides (OCPs) were screened in stream sediments collected along stream flows close to an industrial area in northwestern Spain. Analyses were performed by extraction with organic solvents followed by gas chromatography-mass spectrometry detection. OCPs such as hexachlorobenzene, hexachlorocyclohexane (alpha and beta isomers) and DDT were detected at levels ranging between 29 and 392 microg/kg indicating there is a moderate to severe pollution in the area even though they were banned a few decades ago.

Environmental geochemistry of the Mt Perry copper mines area,SE Queensland, Australia

Intermittent mining and processing of sulphide ore (pyrite–chalcopyrite) at the abandoned Mt Perry mine from the 1870s has resulted in numerousmine workings, waste dumps, a local drainage system contaminated by acid mine drainage (pH 3.3–4.5) and degradation of local soil and vegetation. Weatheringof sulphidic ore, oxidized waste material, tailings and slags (median of 32 samples: 0.65 ppm Au, 17 ppm Ag, 48 ppm As, 3090 ppm Cu, 3.5 wt% Fe, 138 ppm Mn, 19 ppm Mo, 55 ppm Pb, 39 ppm Zn) has led to the formation of secondary minerals (e.g. goethite, hematite, Cu carbonates, gypsum, jarosite, natrojarosite, chalcanthite) on waste materials, stream sediments and stream banks. Waters emanatingfrom underground workings and draining waste dumps have pH values as low as 3.3 and contain elevated contents of As, Cu, Fe, Zn and SO 4 . Dilution from uncontaminated tributaries and groundwaters causes decreasing Cu and Zn concentrations in stream waters, whereas Fe and As precipitate close to the mine site due to adsorption and coprecipitation processes. While much of the dissolved metal load derives from the mine site, Cu is also dissolved out of contaminated stream sediments. Soils in the mines area have elevated Cu and Fe values compared to background soils. The soils acquired their metal enrichments by hydromorphic dispersion from the dissolution of metal-rich particulates, transport of dust and physical erosion of metal-rich particulates from the dumps, and perhaps atmospheric fall-out from smelting plant emissions. Levels of Ag, As, Cu, Fe, and Zn in the fine fraction of stream sediments exceed background values by one to three orders of magnitude. This enrichment has been caused by physical erosion of metal-bearing minerals from abandoned ore and waste dumps and adsorption and coprecipitation of dissolved metals and metalloids in the stream bed. Areas disturbed by mining are characterized by lack of native vegetation, selective and non-selective bioaccumulation of metals and metalloids into plants (gold fern Pityrogramma austroamericana ; hickory wattle Acacia aulococarpa ; bunch speargrass Heteropogon contortus ; wiregrass Aristida benthamii , A. caput-medusae ), and partial recolonization by metal-tolerant plant species (gold fern; bunch speargrass; couch grass, Cynodon dactylon ; swordsedge, Lepidosperma sp.).

Heavy metal assessment in sediments of the Ave river basin (Portugal) by energy-dispersive x-ray fluorescence spectrometry

Anthropogenic activities have contaminated stream sediments around the world with toxic metals. In Portugal, the Ave river basin, draining to the northwestern Portuguese shelf, is heavily contaminated. The Ave river course and its tributaries are located in one of the most populated regions of the country with intensive agricultural and industrial activities, which effluents have been discharged directly into the local stream. This paper reports results obtained in the analysis of superficial sediments collected at the Ave estuary and along the river course within a distance of about 50 km during February 1993. In order to account for seasonal variabilities occurring in the estuary, stations located in this region were also sampled in August 1993. A total of 16 sediment samples were analysed as pressed pellets by energy-dispersive X-ray fluorescence spectrometry for 15 elements. The trend of the elemental contamination was evaluated as a function of the location, taking into account external factors that may influence that distribution (tributaries, industries, etc.) and anthropogenic contributions were identified. Comparison of our data with published values considered as the background for non-polluted sediments (average shale) were carried out by calculating enrichment factors. The latter proved that sediment contamination by Zn and Pb exists all over the river basin and also by Cr and Cu in two regions of the area studied. A general depletion in Ni was measured. No significant seasonal variabilities were detected. © 1998 John Wiley & Sons, Ltd.

Natural Background Determination and Impact Quantification in Trace Metal-Contaminated River Sediments

Historic and current mining activities have contaminated stream sediments around the world with toxic heavy metals. A general lack of premining baseline data makes it difficult to quantify the extent of contamination and to set realistic remediation goals. These problems can be solved by modeling the downstream dispersion of metal anomalies based on dilution mixing of anomalous and tributary sediments. The model allows calculation of the dispersion curves of metals in stream sediments both before and after mining and also allows the quantification of any anthropogenic exaggeration of an anomaly. Mining activities were found to amplify naturally occurring metal anomalies up to 3 orders of magnitude, extending downstream dispersion trains from a natural limit of around 20 km to as much as 500 km. The dilution mixing model provides a useful tool for calculating premining dispersion trains and quantifying the effects of mining on a river basin. Such information is relevant to the understanding, litigation, and remediation of contaminated rivers around the world.

The influence of channel morphology on the chemical partitioning of Pb and Zn in contaminated river sediments

The chemical partitioning of Pb and Zn was investigated in contaminated stream sediments from the River Ystwyth in mid-Wales, with changes in metal/substrate fixation being related to variations in channel morphology. Confinement of the channel by bedrock (chute zones) is sufficient to create very turbulent flow conditions facilitating the precipitation of Mn(IV) on surfaces of sand sized particles (2000-63 μm). Phase specific extraction of Pb (easily reducible fraction) from this particle size range indicates significant adsorption on precipitated forms of Mn. Conversely, under meandering conditions, association with the moderately reducible fraction (Fe-oxides) was more influential in the physico-chemical partitioning of Pb. Thus oxyhydroxide “precipitation zones” are created which affect heavy metal partitioning. These phenomena are, however, not observed on silt and clay sized particle coatings (<63 μm). The partitioning of Zn is not influenced by channel morphology due to a combined influence of the greater solubility of ionic species and subsequent transfer in solution and to the prevalence of total sediment Zn as sphalerite (ZnS).

Chemical and physical partitioning in contaminated stream sediments in the River Ystwyth, Mid-Wales

This study investigates contemporary fluvial contamination of stream sediments by Pb, Zn and Cu from a mine near Aberystwyth, Wales. Of particular interest is the association between metal cations and particulate substrates and which is investigated using a selective extraction procedure. Emphasis is also placed on the difference between adsorptive phases depending on particle size. As particle size decreases the labile phase becomes dominant, with the easily and moderately reducible fraction being the major scavenging agent of soluble cations. Zinc and copper are largely held as residual rock or ore particles and are therefore expected to have a longer residence time in sediments. Recent floodplain development is difficult to interpret due to reworking of upstream metal-rich alluvium. However evidence is presented to suggest that once silt and clay size particles enter the main channel they are largely removed from the system.

Geochemical Analysis of Stream Sediments as a Tool for Environmental Monitoring: A Pigyard Case Study

A geochemical analysis of 11 chemical elements in stream sediments in the vicinity of a pig farm shows that geochemical exploration methods can be used for regional environmental monitoring of organic pollution. In a 5-sq-mi (12.95 km 2 ) area in southern Ontario, contaminated stream sediments showed definite increases in Mg, Ca, Na, K, and Zn. Changes in Cu content were inconclusive; Pb, Co, Ni, Fe, and Mn showed background averages. The study showed that stream sediments are affected by large-scale agricultural operations within a short period of time. It is conclusive that ground water will be affected as contamination continues.