Sediment Ingestion Research Articles

A REVIEW OF CASES OF GEOPHAGY IN CORVIDS (AVES: CORVIDAE) AND A NEW REPORT OF GEOPHAGY IN AZURE JAY (Cyanocorax caeruleus)

Geophagy is the intentional ingestion of soil or sediments by different animal species. In birds this behaviour has been widely reported in Psittacidae and Columbidae, but less so for other families, such as Corvidae. The goal of the present study was to review cases of soil ingestion by corvids and also report a new observation of geophagy in Azure Jay ( Cyanocorax caeruleus ). Geophagy was mentioned only for 11 of the 130 species of the familiy Corvidae, and there is a particular scarcity of reports for Neotropical species. On 26 August 2018 an adult individual of Azure Jay was observed removing and ingesting pieces of dry clay from a nest of Rufous Hornero ( Furnarius rufus ). Hypotheses about this behaviour include mineral supplementation and grinding of food.

Repeated selective enrichment process of sediment microbiota occurred in sea cucumber guts.

Deposit-feeding sea cucumbers repeat ingestion of sediments and excretion of faeces daily and consequently increase bacterial abundance in sediments and promote organic matter mineralization. Such ecological roles are expected to be collaborative activities of sea cucumbers and the gut microbiota. Here, we performed a spatiotemporally broad 16S rRNA gene analysis using 109 samples from sea cucumber faeces and habitat sediments to explore potential contribution of their gut microbiota to the ecological roles. Most operational taxonomic units (OTUs) observed in the faecal samples were shared with the sediment samples, nevertheless faecal and sediment microbiota differed from each other in UniFrac analysis. Lower bacterial diversity and increased relative abundance of specific OTUs in the faecal microbiota strongly suggest selective enrichment of ingested sediment microbiota in their guts. Interestingly, representative faecal OTUs were more abundant in sea cucumber-populated sediments than in un-inhabited sediments, indicating bacteria selectively enriched in the guts were spread on ambient sediments via faeces. Moreover, the predicted microbial community metabolic potential showed a higher abundance of genes related to carbohydrate and xenobiotics metabolisms in faeces than in sediments. Our study suggests the repeated selective enrichment transforms ambient sediment microbial communities and maintains the host's ecological roles by promoting organic matter mineralization.

Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

Mystacodon selenensis Lambert, Martínez-Cáceres, Bianucci, Di Celma, Salas-Gismondi, Steurbaut, Urbina & Muizon, 2017 is a toothed mysticete that represents the earliest member of the suborder in the current state of knowledge. Its holotype is a relatively complete skeleton from the upper Eocene (early Priabonian, c. 36.4 Ma) Yumaque Member of the Paracas Formation from the southern coast of Peru. The thorough description of this specimen is presented here and reveals numerous similarities with the contemporaneous basilosaurids including the retention of an innominate that originally articulated to the unpreserved hind limb. However, several characters of M. selenensis clearly relate this taxon to the mysticetes, such as the large palate with a dorsoventrally flattened rostrum, the posterior extension of the palate with an infraorbital plate of the maxilla, the shortening of the premaxillary part of the rostrum, the zygomatic process of the squamosal being closely apposed to the postorbital process of the frontal, and the humeral head being oriented more proximally than posteriorly. A parsimony analysis retrieves Mystacodon as the earliest diverging branch of the Mysticeti with no close phylogenetic relationship with Llanocetus the second oldest known mysticete (c. 34.2 Ma). The dental formula of M. selenensis is that of basilosaurids (I 3/3, C 1/1, P 4/4, M 2/3). The anterior teeth (incisors and canine) are distinctly proportionally smaller than in basilosaurids, whereas the cheek teeth are very close in relative length, but are relatively larger than in most other toothed mysticetes (except Coronodon). The large cheek teeth of Mystacodon suggest a raptorial feeding strategy, probably assisted with some degree of suction, as indicated by the large size of the palate. The anterior teeth of the holotype display a subhorizontal apical wear facet and the cheek teeth a moderately sloping wear surface, differing from the subvertical attrition facets of basilosaurids. This pattern suggests an efficient dental abrasion resulting from feeding upon abrasive food items or/and from the ingestion of sediment during prey capture, which could indicate some degree of bottom feeding. On the forelimb, the size and orientation of the acromion, the great length of the deltopectoral crest, the massiveness of the olecranon of the ulna, and the strong radial anterior process indicate powerful shoulder movements, which suggest an active use of the forelimb when foraging for food on the sea floor. The robustness of digits and the pachyosteosclerosis of ribs with pestle-like distal end corroborate such a scenario. Mystacodon selenensis represents a first step in the evolutionary history of feeding adaptations of early mysticetes; the latter are likely to have experimented an abundant set of feeding strategies and were probably very eclectic in prey choice and capture before hyperspecialized filter feeding became widespread in the suborder.

Detection of trace elements in freshwater macrobenthic invertebrates of different functional feeding guilds: A case study in Northeast Italy

Trace elements are common contaminants in aquatic ecosystems; their detection in biota yields information on their availability in the environment and provides an indirect indication of freshwater ecological status. We analyzed samples of freshwater macrobenthic invertebrates from six watercourses in Friuli Venezia-Giulia (Northeast Italy) to verify whether trace elements accumulation is related to their ecological status sensu Water Framework Directive (WFD), and to determine tropic level influences on the accumulation of 18 trace elements in macrobenthic communities. Observed concentrations could be in line with results of ecological status assessment defined by the WFD, in fact two sites classified as “Moderate” had the highest trace elements content. The genus Calopteryx (Odonata, predator) was positively correlated with Be, Cr, Fe, Mn, Mo, Ni, Sn, and V (ρS range 0.777–0.844). Positive correlations were also determined for the genus Rhyacophila (Trichoptera, predator) with Cu (ρS=0.757), suggesting bioaccumulation in macroinvertebrate tissue. Ephemeroptera of the genus Caenis (collector-gatherers) were positively correlated with Be, Fe, Mn, Pb, Sb, and V (ρS range 0.757–0.802), indicating that ingestion of sediment is the most effective uptake of these metals.Results of this study, albeit preliminary, showed that trace elements detection in aquatic macrobenthic invertebrates is a useful analysis for obtaining information about the status of freshwater course. Our study provides evidence for a greater accumulation of trace elements in predators and collector-gatherers, suggesting that the tropic level of macrobenthic communities influence the accumulation of trace elements.

Mercury and methylmercury bioaccumulation in a contaminated bay

The bioaccumulation and the main source of total Hg (THg) and methylmercury (MMHg) in the deposit-feeding polychaete Neanthes japonica collected in Jinzhou Bay, China, were investigated. Compared with the historical data, THg bioaccumulation in polychaetes collected in sediment of Jinzhou Bay was distinctly higher due to higher sediment THg concentration, but MMHg bioaccumulation was significantly lower. THg accumulation in polychaetes mainly derived from its accumulation in sediment. However, MMHg bioaccumulation in polychaetes did not correlate with Hg concentration in sediment. Besides sediment ingestion, MMHg accumulation in polychaetes may partially source from the process of in vivo transformation. The in vivo Hg methylation may take place in polychaetes, according to the excellent correlation between MMHg concentration and THg and inorganic Hg concentration in polychaetes. The biochemical characters in polychaete body, the oxidation-reduction environment and the microbial activity in polychaete gut may be beneficial to in vivo Hg methylation.

Sediment microbial assemblage structure is modified by marine polychaete gut passage.

Invertebrate activities in sediments, predominantly the redistribution of particles and porewater, are well-known to regulate the structure of associated microbial assemblages; however, relatively little attention has been given to the effects of sediment ingestion, gut passage and excretion by deposit-feeding invertebrates. Here, we use high-throughput sequencing and quantitative PCR to examine how passage through the gut of the marine polychaete Hediste diversicolor affects the structure of bacterial and archaeal assemblages and the abundance of nitrogen cycling taxa. We show that the digestive tract of H. diversicolor contains unique transitory microbial assemblages that, during gut passage, become more like the surrounding sediment assemblages. Enrichment of similar microbial taxa in both the hindgut and the burrow wall suggest that these transitory gut assemblages may influence the composition of the local sediment community. The hindgut of H. diversicolor also forms a reservoir for unique ammonia-oxidising archaeal taxa. Furthermore, distinct microbial assemblages on external polychaete surfaces suggest that deposit-feeding invertebrates act as vectors that transport microbes between sediment patches. Collectively, these findings suggest that the passage of sediment and associated microbial assemblages through the gut of deposit feeding invertebrates is likely to play a significant role in regulating sediment microbial assemblages and biogeochemical functioning.

Bioaccumulation of 137Cs in anuran larvae utilizing a contaminated effluent canal on the U.S. Department of Energy's Savannah River Site

As a result of activities such as nuclear weapons testing, nuclear power generation and waste disposal, and nuclear accidents, radiocesium (137Cs) is a widely distributed radio-contaminant of concern that readily accumulates in exposed wildlife. Although bioaccumulation of 137Cs is an important factor for understanding its fate within the environment, there are currently limited data available on bioaccumulation patterns of 137Cs in amphibians, despite their widespread distribution and potential to transport contaminants between aquatic and terrestrial ecosystems. Therefore, the objective of this study was to determine the amount of time necessary for anuran larvae experimentally placed in a contaminated system to reach a steady-state whole-body 137Cs concentration, and to determine the threshold at which that steady-state 137Cs concentration occurred for tadpoles within our study system. By restricting uncontaminated bullfrog (Lithobates catesbeianus) larvae to three experimental enclosures located along a137Cs contaminated effluent canal on the U.S. Department of Energy's Savannah River Site, we modeled 137Cs uptake through time using the von Bertalanffy modification of the Richards Model. The results of our modified Richards Model indicate that bullfrog tadpoles achieved steady-state 137Cs concentrations of 3.68–4.34 Bq/g137Cs dry whole-body weight after 11.63–15.50 days of exposure among sampling sites, with an average of 3.94 Bq/g after 14.07 days exposure. Radiocesium accumulation in bullfrog tadpoles was more rapid than that reported for other biota studied from other contaminated systems, likely due to incidental ingestion of sediments and a diet consisting of periphyton and other items that accumulate high levels of 137Cs. Given their rapid accumulation of 137Cs and inability to leave aquatic environments prior to metamorphosis, our data suggest amphibian larvae may be useful indicators for monitoring 137Cs distributions and bioavailability within aquatic systems.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g−1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms.

Dredging-induced turbid plumes affect bio-irrigation and biogeochemistry in sediments inhabited by Lanice conchilega (Pallas, 1766)

Abstract Building man-made structures in coastal seas are often preceded by dredging operations, inducing turbid plumes of suspended sediment. To study the effects of such high-concentration sediment plumes on the suspension-feeding polychaete Lanice conchilega, a laboratory experiment was performed, in which individuals of L. conchilega were exposed to natural seawater with a suspended sediment concentration (SSC) of ∼ 0.3 g l−1 and treatments with elevated SSC of 5 and 1 g l−1, representing concentrations in a dredging plume at the moment of sediment release and after initial dilution, respectively. We measured clearance rates of sediment particles, biogeochemical fluxes, and bio-irrigation. While clearance rates and nitrite efflux significantly increased in both treatments with elevated SSC compared with the control, bio-irrigation increased at 1 g l−1 but was lowest at 5 g l−1. It is suggested that piston pumping is intensified under intermediate concentrations to remove sediment, but ceases under high concentrations are due to sediment ingestion. By transporting oxygen into the sediment, bio-irrigation enhances aerobic microbial processes, among which nitrification. We conclude that short-term extreme suspended sediment concentrations can have a significant impact on the biogeochemistry of the seabed through changes in behaviour of L. conchilega.

Size-selective feeding of Arenicola marina promotes long-term burial of microplastic particles in marine sediments

Despite of their ubiquitous distribution in marine sediments, the role of benthic fauna in microplastic transport at the sea floor has received little attention yet. The present study investigated the influence of bioturbation activity of the polychaete Arenicola marina on microplastic transport and burial in marine sediments. Sediment ingestion was assessed in a long term mesocosm experiment with exposure times ranging from 106 to 240 days, using three particle tracers with different particle diameters (microplastic: 500 and 1000 μm, respectively; luminophores: 130 μm). Sediment grain size distributions were assessed after experiment termination in all feeding layers at 8–12 cm depth to determine the influence of size-selective feeding of A. marina on median grain size and microplastic retention. Burial of microplastic occurred in all mesocosms up to a depth of 20 cm and was strongly dependent on individual sediment feeding rates. For low bioturbation conditions, both microplastic and luminophore concentrations exhibited an exponential decrease with increasing sediment depth, indicating particle burial via feeding funnel transport. Particle concentrations remained high in the uppermost 4 cm of the sediment. At high bioturbation rates, no microplastic particles remained in near-surface sediment layers, but a distinct accumulation of microplastic was observed in the feeding layer, suggesting the discrimination of plastic particles during feeding. In contrast, luminophores displayed a similar accumulation, but additionally showed uniform distributions above feeding layers, indicating ingestion and defecation by polychaetes. In accordance with these findings, an overall coarsening of median grain sizes was observed in all feeding layers, indicating the retention of large microplastic due to size-selective feeding. These findings demonstrate the ability of the conveyor belt-feeding polychaete A. marina to promote unidirectional transports of microplastic ≥500 μm and the potential for the long-term retention of these particles in marine sediments.

Assimilation efficiency of sediment-bound PCBs ingested by fish impacted by strong sorption.

Uptake of polychlorinated biphenyls (PCBs) by fish is controlled by the bioavailability of ingested PCBs in the gut and the freely dissolved concentration in the water moving across the gills. The prediction of bioaccumulation in fish relies on models that account for these exposure routes; however, these models typically do not account for incidental ingestion of sediment by fish, which is not well studied. The literature values for the PCB assimilation efficiency in the gut have been reported for compounds in food matrices and not associated with sediment particles. It is also unclear how mitigation strategies that alter PCB bioavailability in sediments affect predictions made by the bioaccumulation models when sediment ingestion is involved. To test the bioavailability of PCBs from treated and untreated sediments, dietary assimilation efficiencies were measured for 16 PCB congeners in mummichogs (Fundulus heteroclitus) that were fed 4 experimental diets. Diets consisted of PCB-spiked earthworms, spiked untreated sediment mixed with earthworms, spiked activated carbon-treated sediment mixed with earthworms, and spiked activated carbon mixed with earthworms. Assimilation efficiencies were determined by calculating the ratio of PCB mass in the fish tissue to the PCB mass in the food after a pulse feeding experiment. Assimilation efficiencies of PCBs associated with earthworm diet were similar to the values reported in the literature. Fish that were fed the PCB-spiked untreated sediment and activated carbon particles exhibited the highest and lowest assimilation efficiencies, respectively, over a wide KOW range. Assimilation efficiencies of sediment-bound PCBs were significantly reduced (31-93% reduction for different congeners) after amendment with activated carbon. The present study indicates that assimilation of PCBs can be reduced by sorption to black carbon. Environ Toxicol Chem 2017;36:3480-3488. © 2017 SETAC.

Distribution, characterization, and human health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in Ovia River, Southern Nigeria.

The levels and distribution of polycyclic aromatic hydrocarbons (PAHs) in surface water, sediment, and fish (Clarias gariepinus) samples from Ovia River, Southern Nigeria, were evaluated, to assess the contamination profile, dietary intake, and human health risks associated with exposure. Results showed that naphthalene, acenaphthylene, and fluoranthene were the most dominant contaminant in water, sediment, and fish, respectively, with mean concentrations (μg/L) of 3.08, 45.4, and 90.7. Spatial distribution showed high occurrence of PAHs in Ekenwan, the downstream station, for all the matrices. Source identification using multivariate analysis revealed mixed patterns of pyrogenic and petrogenic origins. Estimated daily intake (EDI) of PAHs through fish consumption ranged from 2.18×10-7 to 5.23×10-5mg/kg/day; values were however lower than the reference dose (RfD) indicating low risk. Estimated values for hazard quotients (HQs) and hazard index (HI) for both non-carcinogenic and carcinogenic risks were below 1 indicating low risk through dietary and non-dietary exposure to water, sediment, and fish from Ovia River. However, estimated HI values for direct ingestion of sediment were above 1, indicating the possibility of non-carcinogenic health risk from exposure. Carcinogenic risk indices also indicated low risk from fish consumption. In spite of the assessed low risk from exposure, continuous monitoring of PAH levels in this water body is imperative to prevent future human health effects.

The Daphnia magna role to predict the cadmium toxicity of sediment: Bioaccumlation and biomarker response

To evaluate Daphnia magna role to predict the Cd toxicity in contaminated sediment, the Cd accumulation, metallothionein (MT), and mortality of D. magna exposed to overlying water system or water–sediment coexistence system were measured. The mortality, Cd accumulation, and MT in D. magna increased with the increasing Cd content in sediment. The Cd accumulation and MT in D. magna exposed to the coexistence system were significantly higher than those exposed to the overlying water system because of the ingestion of Cd-containing sediments by D. magna. However, the mortality did not significantly differ in the two systems, suggesting that mortality was less sensitive than accumulation and MT. The Cd accumulation/MT index can explain why the two systems had the similar mortality but different Cd accumulation and MT. Not all the percentage composition of nonresidual fractions (e.g., exchangeable, carbonate bound, and organic bound phases) significantly correlated with the difference values of Cd accumulation and MT, as well as Cd accumulation/MT. However, these indexes increased with the percentage composition of the nonresidual fractions, indicating that the distribution of Cd chemical fractions is crucial for its bioavailability and biotoxicity.

Fractionation of rare earth and other trace elements in crabs, Ucides cordatus, from a subtropical mangrove affected by fertilizer industry

Fractionation of rare earth elements (REE) and other trace metal concentrations (Th, U, Cd, Cr, Cu, Ni, Pb, and Zn) between mangrove sediments and claw muscles and shells of male crabs (Ucides cordatus) from a subtropical estuary highly impacted by fertilizer industry activities was investigated. This is the first record of REE distribution in these organisms, and the results showed higher accumulations of these metals, U and Th in shells, probably related to the replacement of Ca during molting. Contents of Cd, Cr and Ni were similar in both tissues, but Cu, Zn and Pb were mostly accumulated in the claw muscle with concentrations above those considered safe for human consumption according to the Brazilian legislation. REE fractionation was different in the analyzed tissues being softer in the shells. The results provided evidences that the water absorbed during molting controls the chemistry of REE in shells. In contrast, the chemistry of REE in the claw muscle, in which was observed preferential absorption of light REE, is controlled by diet. REE fractionation obtained for the claw muscles was closely correlated to the observed in the contaminated substrate and in materials related to the production of phosphate fertilizers (contamination source), which supports their transference to this Ucides cordatus tissue without fractionation by the ingestion of sediments. Our results showed the potential use of crab tissues for monitoring REE and trace element sources in mangrove areas, with claw muscle exhibiting the contaminant source fingerprint.

Addressing Emerging Risks: Scientific and Regulatory Challenges Associated with Environmentally Persistent Free Radicals.

Airborne fine and ultrafine particulate matter (PM) are often generated through widely-used thermal processes such as the combustion of fuels or the thermal decomposition of waste. Residents near Superfund sites are exposed to PM through the inhalation of windblown dust, ingestion of soil and sediments, and inhalation of emissions from the on-site thermal treatment of contaminated soils. Epidemiological evidence supports a link between exposure to airborne PM and an increased risk of cardiovascular and pulmonary diseases. It is well-known that during combustion processes, incomplete combustion can lead to the production of organic pollutants that can adsorb to the surface of PM. Recent studies have demonstrated that their interaction with metal centers can lead to the generation of a surface stabilized metal-radical complex capable of redox cycling to produce ROS. Moreover, these free radicals can persist in the environment, hence their designation as Environmentally Persistent Free Radicals (EPFR). EPFR has been demonstrated in both ambient air PM2.5 (diameter < 2.5 µm) and in PM from a variety of combustion sources. Thus, low-temperature, thermal treatment of soils can potentially increase the concentration of EPFR in areas in and around Superfund sites. In this review, we will outline the evidence to date supporting EPFR formation and its environmental significance. Furthermore, we will address the lack of methodologies for specifically addressing its risk assessment and challenges associated with regulating this new, emerging contaminant.

Trait-based modelling of bioaccumulation by freshwater benthic invertebrates

Understanding the role of species traits in chemical exposure is crucial for bioaccumulation and toxicity assessment of chemicals. We measured and modelled bioaccumulation of polychlorinated biphenyls (PCBs) in Chironomus riparius, Hyalella azteca, Lumbriculus variegatus and Sphaerium corneum. We used a battery test procedure with multiple enclosures in one aquarium, which maximized uniformity of exposure for the different species, such that the remaining variability was due mostly to species traits. The relative importance of uptake from either pore water or sediment ingestion was manipulated by using 28 d aged standard OECD sediment with low (1%) and medium (5%) OM content and 13 months aged sediment with medium OM (5%) content. Survival was ≥76% and wet weight increased for all species. Reproduction of H. azteca and weight gain of H. azteca and S. corneum were significantly higher in the medium OM aged sediments than in other sediments, perhaps due to a more developed microbial community (i.e., increase in food resources). Biota-sediment accumulation factors (BSAF) ranged from 3 to 114, depending on species and PCB congener, with C. riparius (3–10)<S. corneum (10–17)≤L. variegatus (7–61)≤H. Azteca (5–114), thus challenging the presumed value of 1–2 typically employed in ecological risk assessment schemes. BSAFs for freshwater taxonomic groups were compared with their marine counterparts and showed overlapping values. The dynamic bioaccumulation model with species-specific bioaccumulation parameters fitted well to the experimental data and showed that bioaccumulation parameters were depended on species traits. Enclosure-based battery tests and mechanistic BSAF models are expected to improve the quality of the exposure assessment in whole sediment toxicity tests.

Health risk assessment due to heavy metal exposure from commonly consumed fish and vegetables

Contamination of heavy metals in fish and vegetables is regarded as a major crisis globally, with a large share in many developing countries. In Bogra District of Bangladesh, concentrations of six heavy metals, i.e., chromium (Cr), nickel (Ni), copper (Cu), arsenic (As), cadmium (Cd) and lead (Pb), were evaluated in the most consumed vegetables and fish species. The sampling was conducted during February–March 2012 and August–September 2013. The levels of metals varied between different fish and vegetable species. Elevated concentrations of As, Cd and Pb were observed in vegetable species (Solanum tuberosum, Allium cepa and Daucus carota), and fish species (Anabas testudineus and Heteropneustes fossilis) were higher than the FAO/WHO permissible limits, indicating these three metals might pose risk from the consumption of these vegetable and fish species. The higher concentration of heavy metals in these vegetable species might be due to the higher uptake from soil and sediment ingestion behavior in fish species. Multivariate principal component analysis (PCA) showed significant anthropogenic contributions of Cr, Ni, Cu and Pb in samples as the PCA axis scores were correlated with scores of anthropogenic activities. Target hazard quotients showed that the intakes of Cu, As and Pb through vegetables and fish were higher than the recommended health standards, indicated non-carcinogenic risk. Therefore, intakes of these elements via fish and vegetables for Bangladeshi people are a matter of concern.

Bioaccumulation of perfluorinated carboxylates and sulfonates and polychlorinated biphenyls in laboratory-cultured Hexagenia spp., Lumbriculus variegatus and Pimephales promelas from field-collected sediments

Polychlorinated biphenyls (PCBs) and perfluorinated carboxylates and sulfonates (PFASs) are persistent pollutants in sediment that can potentially bioaccumulate in aquatic organisms. The current study investigates variation in the accumulation of PCBs and PFASs in laboratory-cultured Hexagenia spp., Lumbriculus variegatus and Pimephales promelas from contaminated field-collected sediment using 28-day tests. BSAFlipid (lipid-normalized biota-sediment accumulation factor) values for total concentration of PCBs were greater in Hexagenia spp. relative to L. variegatus and P. promelas. The distribution of congeners contributing to the total concentration of PCBs in tissue varied among the three species. Trichlorobiphenyl congeners composed the greatest proportion of the total concentration of PCBs in L. variegatus while tetra- and pentabiphenyl congeners dominated in Hexagenia spp. and P. promelas. Perfluorooctane sulfonate (PFOS) was present in all three species at concentrations greater than all other PFASs analyzed. Hexagenia spp. also produced the greatest BSAFlipid and BSAFww (non-lipid-normalized biota-sediment accumulation factor) values for PFOS relative to the other two species. However, this was not the case for all PFASs. The trend of BSAF values and number of carbon atoms in the perfluoroalkyl chain of perfluorinated carboxylates varied among the three species but was similar for perfluorinated sulfonates. Differences in the dominant pathways of exposure (e.g., water, sediment ingestion) likely explain a large proportion of the variation in accumulation observed across the three species.

Dietary ingestion of fine sediments and microalgae represent the dominant route of exposure and metal accumulation for Sydney rock oyster (Saccostrea glomerata): A biokinetic model for zinc

Past studies disagree on the extent to which dissolved or dietary uptake contribute to metal bioaccumulation in the filter-feeding Sydney rock oyster (Saccostrea glomerata) in urbanized estuaries. Although most data support the assumption that fine sediments are a major route of metal uptake in these bivalves, some studies based in the Sydney estuary, Australia, have indicated a poor correlation. In the present study, seawater, sediment and microalgae were radiolabelled with 65Zn tracer and exposed to S. glomerata to assess the influence of dissolved and dietary sources to Zn bioaccumulation. Oysters in the dissolved-phase uptake experiment (5, 25 and 50μgL−1 65Zn for 4 d followed by 21 days of depuration) readily accumulated 65Zn for all three concentrations with an uptake rate constant of 0.160±0.006L dry weight g−1d−1. Oysters in the dietary assimilation experiment (1h pulse-feed of either 65Zn-radiolabelled suspended fine-fraction (<63μm) sediment or the microalgae Tetraselmis sp.) accumulated 65Zn, with assimilation efficiencies of 59 and 67% for fine sediment and microalgae, respectively. The efflux rates were low for the three experiments (0.1–0.5%d−1). A bioaccumulation kinetic model predicts that uptake of Zn will occur predominantly through the dietary ingestion of contaminated fine sediment particles and microalgae within the water column, with considerably greater metal bioaccumulation predicted if oysters ingested microalgae preferentially to sediments. However, the model predicts that for dissolved Zn concentrations greater than 40μgL−1, as observed during precipitation events, the uptake of the dissolved phase may contribute ≥50% to accumulation. Overall, the results of the present study suggest that all three sources may be important exposure routes to S. glomerata under different environmental conditions, but contributions from dietary exposure will often dominate.

Experimental investigation on ingestion of sediment into trench weirs

Trench weirs are commonly constructed across boulder rivers. Such weirs have definite advantages, as they do not obstruct the flow of the river, but susceptible to ingestion of bed load sediment having size smaller than clear opening of the rack into the trench. This study deals with the experimental study of the mechanics of movement of sediments, over and across the racks and also quantification of the sediments ingested/trapped into the trench, which shall be useful for fixing the dimensions of the trench weir for minimum ingestion of sediment. This study reveals that the trajectory of the sediments movement and stream lines of flow are different due to different inertia and for the minimization of entry of sediment into the trench, the clear opening length shall be kept less than the jumping length of the particles. For ratio of size of sediment to clear spacing of rack less than 0.75, the total incoming sediment is ingested into the trench. However, for ratio greater than 0.75, the ingested sediment depends on the diverted discharge. A relationship is developed to estimate the percentage of incoming sediment, ingested into the trench. The proposed relationship computes the ingested sediment into the trench within ±3% error.