Assessment of mercury bioavailability to benthic macroinvertebrates using diffusive gradients in thin films (DGT)

Abstract

Mercury-specific diffusive gradient in thin films (DGTs) were used in laboratory microcosms as a biomonitoring tool to assess the lability of mercury (Hg) total and monomethylmercury Hg (MeHg), and to develop a relationship between chemical lability and bioavailability in estuarine sediments. Time-series deployment of DGTs in sediments showed that sediment-bound MeHg is more labile than sediment-bound inorganic Hg. In subsequent experiments, DGTs were deployed simultaneously with three benthic macroinvertebrates (the estuarine amphipod, Leptocheirus plumulosus; the estuarine polychaete, Nereis virens; and the marine clam, Macoma nasuta) in sediments for up to 55 days. All organisms and their co-deployed DGTs exhibited an initial period of rapid Hg uptake followed by slower uptake reaching apparent steady state. Strong correlative relationships were generally observed between paddle-type DGTs and macroinvertebrate tissue data (r(2) between 0.57 and 0.97). Further, %MeHg:Total Hg ratios for M. nasuta and N. virens (38.5 ± 12.2 and 19.2 ± 5.2) were similar to their corresponding ratios for the DGTs (33.1 ± 13.3 and 24.4 ± 11.0), and they were significantly higher than the same ratios for sediment (2.9 ± 0.3) and pore water (8.5 ± 4.9). The %MeHg:Total Hg ratios for L. plumulosus (68.5 ± 6.2) were significantly higher than those for the DGTs. This may be because the tissue and DGT data for this organism were not truly co-located as L. plumulosus burrows close to the sediment surface, and the DGTs sampled the sediment surface. Overall, our results suggest that for benthic macroinvertebrates in estuarine sediments studied here, (a) sediment MeHg is more bioavailable than inorganic Hg, (b) sediment and pore-water concentration measurements are not good predictors for the extent of bioaccumulation of Hg species, and (c) DGTs are an effective biomonitoring tool for the assessment of bioavailability of Hg species.

Critical review of mercury sediment quality values for the protection of benthic invertebrates

“…For example, Lawrence and Mason estimated that steady state is achieved in the amphipod Leptocheirus plumulosus after 50 d, whereas Stephenson and Turner reported that steady state was attained in 14 d by Hyalella azteca . Amirbahman et al found that uptake by L. plumulosus and the bivalve Macoma nasuta plateaued after 14 d, whereas a plateau in uptake in the polychaete Nereis virens was observed after 7 d. In contrast, Kennedy et al found that concentrations appeared to reach steady state for N. virens within 7 d, whereas steady state for M. nasuta was not observed until approximately 70 d to 90 d. For the purposes of the present review, 7 d was considered to be a reasonable minimum exposure duration requirement for quantification of toxicity via whole‐sediment exposures, recognizing that longer exposures could potentially yield more sensitive responses for some species.…”

“…Future analytical refinements to sediment porewater techniques are recommended. Passive sampling methods that involve absorption of labile or dissolved porewater mercury while minimizing the disturbance of sediment physicochemical conditions (e.g., diffusive gradient in thin films using functionalized thiol groups as the binding agent) are likely to aid in understanding mercury in porewater and may be useful as an exposure metric . These tools are still in development and/or may not be as widely (commercially) available as porewater analyses.…”

Quantification of Mercury Bioavailability for Methylation Using Diffusive Gradient in Thin-Film Samplers

“…Therefore, the relevance of this filtered Hg fraction for Hg bioavailability remains uncertain, as suggested by previous reports concluding that filtered porewater Hg content is a poor indicator of Hg bioavailability. 15 − 17 , 29 , 35 …”

Diffusive gradients in thin films for predicting methylmercury bioavailability in freshwaters after photodegradation

“…This technique is widely used for passive sampling of trace metals, and allows the determination of timeweighted average concentrations of bioavailable contaminant species (Cusnir et al, 2014). The DGT technique has been successfully used for in situ determination of kinetically labile metal species in aquatic systems, such as MeHg (Clarisse et al, 2012) and is an effective tool for the assessment of bioavailability of Hg species (Amirbahman et al, 2013). The principle of the DGT technique is based on the diffusion of the dissolved species through a diffusive layer and their accumulation in an ion-exchange resin.…”