Heavy metals and arsenic fixation into freshwater organic matter under Gammarus pulex L. influence
Introduction
Contamination of water bodies with heavy metals and metalloids still remains a major concern in most mining sites (Dinelli et al., 2001). The ability of metals and metalloids to dissolve not only at low pH (predominantly as cation) and low Eh but also at neutral to alkaline aerobic milieu (e.g. as carbonate complexes) (Burton et al., 2008) exuberates these concerns. They also occur as organic complex of humic and fulvic acids as part of dissolved organic carbon (DOC) (Zhao et al., 2009) as well as fixed to colloids, and remain mobile. However, there are observations that vegetated water bodies and related organic sediments have higher capacity to immobilize the mobile metals (Dienemann et al., 2006, Ross and Dudel, 2008). Metal and metalloids may accumulate in plant material including leaf litter, which settles on the bottom of the water body and eventually decompose. During decomposition of the organic matter, the metal and metalloids are fixed by particulate organic material (POM) (Guo et al., 2006). Simultaneously, DOC emerged from the decomposition and biofilm eventually colonize the leaf litter. This heterotrophic biofilm is a collection of the individuals of the decomposer community and extra cellular polymeric substances (EPS) (Flemming et al., 1996).
Decomposition of litter in the sediment is accelerated by invertebrate shredders (Robinson et al., 1998, Hoffmann, 2005). Most invertebrates shredder, especially G. pulex L. feeds on litter when the litter is well colonized by primary microbial degrader (e.g. hyphomycetes and bacteria) (Hieber and Gessner, 2002). Species from the genus Gammarus are dominant invertebrates in most freshwater systems of Europe and Central Asia. However, the impact of shredders like G. pulex on metal fixation on POM, as well as the influence of G. pulex on the remobilization of fixed heavy metals from POM has been least investigated. So far, there is only literature on uranium (Schaller et al., 2008), while other co-pollutants from mining-waste damps have never been reported. In view of this, we investigated the influence of G. pulex on the immobilization of a few heavy metals and metalloids in aquatic system, as well as the role of they play on quality of fixation into the organic partition of the sediments. This was done to complement our earlier investigation where the G. pulex and other invertebrate shredders were observed to facilitate release of DOC during composition of litter.
Section snippets
The test organisms
The specimens of Gammarus pulex L., used in experiments, were collected from Prießnitz, a stream in Dresden (Germany). G. pulex was used in the study because it was also found and reported in stream receiving effluents from former uranium mines (Schaller et al., 2009). For acclimatization to the experimental conditions, the individuals of G. pulex were pre-cultured for ten days in the laboratory (in 40 L of tap water, 12–15 °C, ∼100 lux of light intensity for 14 h per day) before starting the
Formation of DOC, POM and FPOM by G. pulex
The formation of POM and FPOM in the experiment was significantly higher in test vessels with G. pulex than those without the invertebrates (p < 0.05) (Fig. 1a and b). Fig. 2a reveals that DOC content increases in both variants. The DOC-level at start was in an oligotrophic to weak eutrophic range (2.43 mg L−1). At the end of the experiment, vessels with G. pulex had the DOC content in ranges observed in eutrophic waters (11.9 ± 0.37 mg L−1) (Schaller et al., 2008).
Impact of decomposing on element fixation
At the end of experiments we found a
Discussion
The results obtained in this study agrees with previously reported that presence of invertebrate shredders facilitate the degradation rate of leaf structure, while at the same time the amount of lower particle sizes of organic matter (POM and FPOM) increases (Tiegs et al., 2008). The POM and FPOM are produced when the G. pulex cut the leaf litter into small particles, ingest some and excrete them (Graca, 2001). The DOC is released during the decomposing, when soluble polymeric organic
Conclusion
Our results reveal that G. pulex facilitate the enrichment of heavy metals in organic partition of sediments by significantly enhancing formation of particulate (POM 400–2000 μm) and fine particulate (FPOM 0.45–400 μm) organic matter. This smaller particle sizes had high surface area which results in increased biofilm development where high amount of metal adsorb. Consequently, invertebrate shredders had a significant effect on initial removal of metals and metalloids in polluted freshwater
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Organic matter degradation and redistribution of sediment associated contaminants by benthic invertebrate activities
2022, Environmental PollutionCitation Excerpt :Specific macroinvertebrate traits may either enhance the flux of contaminants from the sediment to the water column or the other way around, enhance the sedimentation of contaminants. Both shredding and grazing by macroinvertebrates on course particulate organic matter (CPOM) increases the fraction of fine particulate organic matter (FPOM), which creates additional binding sites for metals, resulting in an increased fixation of those metals in organic matter (Schaller & Brackhage, 2015; Schaller et al., 2010). Biodeposition by filter feeders also results in the fixation of contaminants in the sediment, as particle-associated contaminants are filtered from the water column and subsequently deposited as (pseudo)faeces (Gossiaux et al., 1998).
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2015, ChemosphereCitation Excerpt :The mobilization of metals/metalloids (Fig. 2) from organic matter to the water during the experiment with increasing DOC concentrations are in accordance with other studies showing the impact of DOC on element mobilization (Mibus et al., 2007). However, the data contrast with findings from experiments revealing an impact of invertebrate shredders on metal fixation/remobilization with no influence of the DOC level (Schaller et al., 2010a; Schaller and Machill, 2012). This contrast may be explained by a lower fixation capacity of the smaller sizes of POM in the current study, because these smaller sizes of POM contain only feces of the snails and less fragmented leaf litter, compared to studies using invertebrate shredders which contains smaller parts of leaf litter (Schaller et al., 2008, 2010a), which in turn may result in lower amounts of heterotrophic biofilm growing on the smaller sized POM.
Invertebrate shredder as a factor controlling the fixation potential for metals/metalloids in organic matter during decay
2013, Ecological EngineeringCitation Excerpt :The high mobilization at the start could be explained by the unpolluted water used in the experiments, which had to be equilibrated to the high elemental concentrations of the litter. Also the significant but low effect of the invertebrates on elemental release was in accordance with previous experiments (Schaller et al., 2010a). A linkage between DOC release and elemental mobilization can only be suggested for manganese, but with no high correlation coefficient (data not shown).
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2013, Ecological EngineeringCitation Excerpt :The impact of other animal key-species in aquatic ecosystems (apart from invertebrate shredder) on element fixation/remobilization was suggested (Schaller et al., 2011), but the verification is pending. Data from a field experiment reveal that invertebrate shredders facilitate metal and metalloid enrichment into smaller particle sizes of POM even in the presence of high concentrations of DOC (Schaller et al., 2010a; Schaller et al., 2010b). These high DOC levels were expected to bind metals/metalloids (Sachs et al., 2007), but the opposite was shown.
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2013, Science of the Total Environment