Metal Oxides in Surface Sediment Control Nickel Bioavailability to Benthic Macroinvertebrates.

In aquatic ecosystems, the cycling and toxicity of nickel (Ni) are coupled to other elemental cycles that can limit its bioavailability. Current sediment risk assessment approaches consider acid-volatile sulfide (AVS) as the major binding phase for Ni, but have not yet incorporated ligands that are present in oxic sediments. Our study aimed to assess how metal oxides play a role in Ni bioavailability in surficial sediments exposed to effluent from two mine sites. We coupled spatially explicit sediment geochemistry (i.e., separate oxic and suboxic) to the indigenous macroinvertebrate community structure. Effluent-exposed sites contained high concentrations of sediment Ni and AVS, though roughly 80% less AVS was observed in surface sediments. Iron (Fe) oxide mineral concentrations were elevated in surface sediments and bound a substantial proportion of Ni. Redundancy analysis of the invertebrate community showed surface sediment geochemistry significantly explained shifts in community abundances. Relative abundance of the dominant mayfly (Ephemeridae) was reduced in sites with greater bioavailable Ni, but accounting for Fe oxide-bound Ni greatly decreased variation in effect thresholds between the two mine sites. Our results provide field-based evidence that solid-phase ligands in oxic sediment, most notably Fe oxides, may have a critical role in controlling nickel bioavailability.

Nickel Partitioning and Toxicity in Sediment during Aging: Variation in Toxicity Related to Stability of Metal Partitioning.

Metals in sediment can be complexed by minerals, partition between solid and aqueous phases, and cause toxicity at high concentrations. We studied how the oxidation of surface sediment that occurs during aging alters the partitioning and toxicity of Ni. Two sediments (Burntwood and Raisin) were amended with Ni, equilibrated, incubated in a flow-through flume, and examined for sediment physicochemistry and toxicity to Hyalella azteca (7 day growth). Through time, the sediment surface (5 mm) was oxidized, acid-volatile sulfide concentrations declined in Raisin sediment, and amorphous Fe oxides increased. Porewater Ni concentrations declined through time but total Ni concentrations in sediment were unchanged, suggesting changes in Ni partitioning through time. Both sediments elicited a toxic dose-response by H. azteca early in the aging process; but only Burntwood, for which Ni was primarily partitioned to Fe oxide minerals, exhibited a consistent dose-response during aging. Low total Ni concentrations (20 mg kg-1) in Raisin sediment reduced H. azteca growth at initiation, but all Ni treatments (up to 3000 mg kg-1) exhibited similar growth after 12 days of aging. The dynamic toxicity observed in Raisin sediment was likely due to the instability of NiS in surface sediments early in the aging process. These data suggest that short-term toxicity assays with homogenized Ni-amended sediment (i.e., standard sediment toxicity tests) may be accurate for sediments where Ni speciation is dominated by oxidized ligands; however, under high-AVS and high-Fe conditions, calculated toxicity thresholds may be overly conservative (here by >100-fold) with respect to natural sediment conditions.

Microplastic as a Vector for Chemicals in the Aquatic Environment: Critical Review and Model-Supported Reinterpretation of Empirical Studies.

The hypothesis that 'microplastic will transfer hazardous hydrophobic organic chemicals (HOC) to marine animals' has been central to the perceived hazard and risk of plastic in the marine environment. The hypothesis is often cited and has gained momentum, turning it into paradigm status. We provide a critical evaluation of the scientific literature regarding this hypothesis. Using new calculations based on published studies, we explain the sometimes contrasting views and unify them in one interpretive framework. One explanation for the contrasting views among studies is that they test different hypotheses. When reframed in the context of the above hypothesis, the available data become consistent. We show that HOC microplastic-water partitioning can be assumed to be at equilibrium for most microplastic residing in the oceans. We calculate the fraction of total HOC sorbed by plastics to be small compared to that sorbed by other media in the ocean. We further demonstrate consistency among (a) measured HOC transfer from microplastic to organisms in the laboratory, (b) measured HOC desorption rates for polymers in artificial gut fluids (c) simulations by plastic-inclusive bioaccumulation models and (d) HOC desorption rates for polymers inferred from first principles. We conclude that overall the flux of HOCs bioaccumulated from natural prey overwhelms the flux from ingested microplastic for most habitats, which implies that microplastic ingestion is not likely to increase the exposure to and thus risks of HOCs in the marine environment.

Copper Sediment Toxicity and Partitioning during Oxidation in a Flow-Through Flume.

The bioavailability of transition metals in sediments often depends on redox conditions in the sediment. We explored how the physicochemistry and toxicity of anoxic Cu-amended sediments changed as they aged (i.e., naturally oxidized) in a flow-through flume. We amended two sediments (Dow and Ocoee) with Cu, incubated the sediments in a flow-through flume, and measured sediment physicochemistry and toxicity over 213 days. As sediments aged, oxygen penetrated sediment to a greater depth, the relative abundance of Fe oxides increased in surface and deep sediments, and the concentration of acid volatile sulfide declined in Ocoee surface sediments. The total pool of Cu in sediments did not change during aging, but porewater Cu, and Cu bound to amorphous Fe oxides decreased while Cu associated with crystalline Fe oxides increased. The dose-response of the epibenthic amphipod Hyalella azteca to sediment total Cu changed over time, with older sediments being less toxic than freshly spiked sediments. We observed a strong dose-response relationship between porewater Cu and H. azteca growth across all sampling periods, and measurable declines in relative growth rates were observed at concentrations below interstitial water criteria established by the U.S. EPA. Further, solid-phase bioavailability models based on AVS and organic carbon were overprotective and poorly predicted toxicity in aged sediments. We suggest that sediment quality criteria for Cu is best established from measurement of Cu in pore water rather than estimating bioavailable Cu from the various solid-phase ligands, which vary temporally and spatially.

Coupled effects of hydrodynamics and biogeochemistry on Zn mobility and speciation in highly contaminated sediments.

Porewater transport and diagenetic reactions strongly regulate the mobility of metals in sediments. We executed a series of laboratory experiments in Gust chamber mesocosms to study the effects of hydrodynamics and biogeochemical transformations on the mobility and speciation of Zn in contaminated sediments from Lake DePue, IL. X-ray absorption spectroscopy (XAS) indicated that the oxidation of surficial sediments promoted the formation of more mobile Zn species. Bulk chemical measurements of porewater, overlying water, and sediment also suggested that this process liberated aqueous metals to porewater and facilitated Zn efflux to the overlying water. In addition, sediment resuspension events increased the release of aqueous metals to both surficial porewater and the overlying water column. XAS analysis indicated that resuspension increased dissolution of Zn-sequestering mineral phases. These results show that both steady slow porewater transport and rapid episodic resuspension are important to the release of metal from fine-grained, low-permeability contaminated sediments. Thus, information on metals speciation and mobility under time-varying overlying flow conditions is essential to understanding the long-term behavior of metals in contaminated sediments.

Teasing out the Effects of Natural Stressors at Chemically Contaminated Sites.

Aquatic ecosystems are often impacted by a multitude of stressors, many of which are introduced by a combination of anthropogenic activities such as agricultural development, urbanization, damming, and industrial discharge. Determining the primary stressors responsible for ecological impairments at a site can be complex and challenging; however, it is crucial for making informed management decisions. Improper diagnosis of an impaired system can lead to misguided attempts at remediation, which can be both time consuming and costly. We focused on the development, implementation, and evaluation of methodologies that, in combination, allowed us to identify the primary stressors. These included a four-phase, weight-of-evidence (WOE) assessment including in situ Toxicity Identification and Evaluation (iTIE) testing, physicochemical and macrobenthos characterization, reciprocal sediment transplants, and laboratory and in situ toxicity testing. The contaminants of concern (COCs) at the site were elevated levels of ammonia, chloride, pH, and total dissolved solids in groundwater upwellings into a high-quality waterway. Reciprocal transplants of site sediments and nearby reference sediments and traditional benthic sampling showed impaired benthic indices and multiple stations around a contaminated industrial settling basin. Impaired stations had elevated COCs in groundwaters but exhibited a steep vertical concentration gradient, with concentrations decreasing near the sediment-surface water interface. We describe Phase 4 of the study, which focused on teasing out the role of dissolved oxygen sags in benthic macroinvertebrate responses. Extensive submerged and emergent macrophytes, algae, and cyanobacteria co-occurred at the impaired sites and increased throughout the summer. Laboratory testing suggested that ammonia and pH were possibly toxic at the sites, based on groundwater concentrations. The in situ toxicity testing, however, showed toxicity occurring even at stations with low levels of COCs concurrently with large diurnal fluxes in dissolved oxygen (DO). A final phase using a type of iTIE approach utilized limnocorrals with and without aeration and with in situ toxicity measures using Hyalella azteca. The Phase 4 assessment revealed that low DO levels were primarily responsible for impaired benthic communities, and COC upwellings were diluted at the sediment-water interface to nontoxic levels. These findings will allow for improved management decisions for more efficient and effective restoration activities. Environ Toxicol Chem 2024;43:1524-1536. © 2024 SETAC.

Has the Rio Doce "time bomb" been defused? Using a weight-of-evidence approach to determine sediment quality.

The Fundão mine tailings dam rupture of 2015, in the Rio Doce basin, Brazil, resulted in the deposition of tailings downstream of the dam. It has yet to be determined if metals associated with the tailings have contributed toxicity to organisms, burying a time bomb that could be ticking. Currently the data on toxicity to benthic and aquatic organisms have not been assessed sufficiently to allow an informed assessment using an approach based on weight-of-evidence. This study was conducted to ascertain if sediments at "hot spots" that received Fundão tailings reflected elevated concentrations of metals and if these concentrations were sufficient to result in toxicity to freshwater organisms. The lines-of-evidence considered included assessing metals concentrations in relation to sediment quality criteria, establishing biogeochemical characterizations, completing an evaluation of potential metal release upon resuspension to provide information on bioavailability, and identifying acute and chronic toxicity effects using sensitive native species for waters (water flea, Daphnia similis) and sediments (burrowing midge larvae, Chironomus sancticaroli). Only porewater concentrations of iron and manganese exceeded Brazilian surface water criteria, whereas most trace elements exhibited no enrichment or elevated environmental indexes. The concentrations of bioavailable metals were assessed to be low, and metal concentrations did not increase in the overlying water upon resuspension; rather, they decreased through time. Toxicity testing in resuspended waters and bulk sediments resulted in no acute or chronic toxicity to either benthic or aquatic species. The low metal bioavailability and absence of toxicity of the tailings-enriched sediments was attributed to the strong binding and rapid removal of potentially toxic metal ions caused by oxyhydroxides and particles in the presence of iron-rich particulates. The findings of these sediment hot-spot studies indicate the Fundão dam release of tailings more than six years ago is not causing the current release of toxic concentrations of metals into the freshwaters of the Rio Doce. Integr Environ Assess Manag 2024;20:148-158. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Evaluating the performance of diffusive gradients in thin films for predicting Ni sediment toxicity.

Diffusive gradients in thin films (DGTs) rapidly measure labile fractions of metal and are promoted as an assessment tool for bioavailability. Using macroinvertebrate community composition as a response, this study compared the predictive ability of DGT-measured Ni with acid volatile sulfide (AVS) and organic carbon (OC) corrected Ni [(SEM(Ni)-AVS)/f(OC)] and total Ni concentrations. In two experiments, sediments were amended with Ni and placed within either a streamside mesocosm or deployed in situ. DGT-measured Ni concentrations (C(DGT)) increased with increasing total Ni, were greater at depth, and decreased over time. Relationships between Ni C(DGT) and sediment geochemistry indicated a shift in Ni partitioning from AVS-bound to Fe- and Mn-associated Ni. In both experiments, DGT-measured Ni poorly predicted the invertebrate response to metal, whereas models that included total Ni or (SEM(Ni)-AVS)/f(OC) effectively predicted the invertebrate response for the streamside mesocosm and in situ experiments, respectively. C(DGT) overestimated the available Ni fraction, possibly due to sampling either nonbioavailable solid-phase Ni or Ni irrespective of cations competing at the biotic ligand. We suggest that C(DGT) cannot replace (SEM(Ni)-AVS)/f(OC) for predicting invertebrate response to sediment Ni, and greater understanding of metal species lability to DGTs is needed before assuming equivalence between bioavailable and DGT-labile metals in sediments.

Interactive effects of phosphorus and copper on Hyalella azteca via periphyton in aquatic ecosystems.

This research examined the interaction between dissolved copper and phosphorus, with respect to their effects on the freshwater amphipod Hyalella azteca feeding on periphyton. Field-collected periphyton communities were exposed to different nutrient and metal conditions in indoor recirculating streams. H. azteca were then exposed to water and periphyton from these streams. There was rapid Cu accumulation by periphyton but the total Cu concentration of periphyton was not directly related to dissolved P. In terms of H. azteca growth, an interactive effect was found between Cu and P as growth was reduced more than expected in the low Cu-high P treatment. Our data suggest that eutrophic conditions result in greater Cu toxicity to benthic macroinvertebrates at lower metal concentrations, likely due to higher assimilation efficiency of dietary Cu from periphyton incubated under eutrophic conditions. These results imply that non-additive interactions between multiple stressors may cause ecosystem effects as detected in standard laboratory bioassays conducted under controlled conditions.

Evaluation of Capping Materials to Reduce Zinc Flux from Sediments in a Former Mining Pit Lake.

Wilson Mine is a former vanadium mine site located in the Ouachita Mountains near Hot Springs, Arkansas. The site, which drains via two streams to Lake Catherine, has undergone extensive reclamation to significantly reduce groundwater and surface water contact with mine spoils. One of the streams passes through a former mine pit forming East Wilson Pond, and flux from pit lake sediments can result in elevated metal, that is, zinc (Zn), concentrations in overlying water. To mitigate potential risks, an investigation was conducted to evaluate the efficacy of capping materials for partitioning Zn-contaminated sediments from overlying water in East Wilson Pond. A 28-day laboratory study compared the effectiveness of capping materials including combinations of limestone, bentonite clay, and gravel for mitigating Zn flux, including under reasonable worst-case conditions (pH 5.5) encountered in the hypolimnion. Dissolved Zn was monitored over time in overlying water and in sediment porewaters within untreated controls and within the capping layer of treated systems. The use of limestone and/or bentonite clay improved buffering capacity compared to the noncapped control, and pH declined gradually but only modestly in the overlying water and porewater of all treated systems. Concentrations of Zn in overlying water of the noncapped control increased from approximately 30 to 100 µg/L during the study period, while concentrations in the overlying water and porewater of systems containing capping materials remained low (10-30 µg/L). The results demonstrated the effectiveness of the capping materials for neutralizing pH and reducing Zn flux, and a three-layer cap consisting of limestone (top) + bentonite clay (middle) + gravel (bottom) was determined to be most effective. These results were used to inform the selection of materials for the application of a cap to reduce Zn flux from the pit lake sediments. Environ Toxicol Chem 2022;41:193-200. © 2021 SETAC.

Nickel phase partitioning and toxicity in field-deployed sediments.

The pool of bioavailable metal in sediments can be much smaller than total metal concentration due to complexation and precipitation with ligands. Metal bioavailability and toxicity in sediment is often predicted from models of simultaneous extracted metal and acid volatile sulfide (SEM-AVS); however, studies of the applicability of these models for Ni-contaminated sediments have been conducted primarily in laboratory settings. We investigated the utility of the SEM-AVS models under field conditions: Five lotic sediments with a range of sulfide and organic carbon contents were amended with four concentrations of Ni, deployed in streams for eight weeks, and examined for colonizing macroinvertebrates. After four weeks, colonizing macroinvertebrates showed a strong negative response to the Ni-treated sediments and SEM-AVS models of bioavailability differentiated between toxic and nontoxic conditions. By Week 8, relationships deteriorated between colonizing macroinvertebrates and SEM-AVS model predictions. Total Ni in the sediment did not change through time; however, Ni partitioning shifted from being dominated by organic cabon at deployment to associations with Fe and Mn. Combined geochemical and toxicity results suggest that Fe and Mn oxides in surface sediments resulted in Ni being less available to biota. This implies that current SEM-AVS models may overestimate bioavailable Ni in sediments with oxic surface layers and sufficient Fe and Mn.

A Novel In Situ Toxicity Identification Evaluation (iTIE) System for Determining which Chemicals Drive Impairments at Contaminated Sites.

Human-dominated waterways contain thousands of chemicals. Determining which chemical is the most important stressor is important, yet very challenging. The Toxicity Identification Evaluation (TIE) procedure from the US Environmental Protection Agency uses a series of chemical and physical manipulations to fractionate compounds within a matrix and systematically identify potential toxicants through laboratory bioassay testing. Although this may provide useful information, it lacks ecological realism because it is subject to laboratory-related artifacts and is resource intensive. The in situ Toxicity Identification Evaluation (iTIE) technology was developed to improve this approach and has undergone a number of modifications over the past several years. The novel prototype 3 consists of an array of iTIE ambient water fractionation units. Each unit is connected to a peristaltic pumping system with an organism exposure chamber that receives water from a resin chamber to chemically fractionate test site water. Test organisms included freshwater and marine standard toxicity test species. Postfractionation waters are collected for subsequent chemical analyses. Currently, the resins allow for separation of ammonia, metals, and nonpolar organics; the subsequent toxicity responses are compared between treatments and unfractionated, ambient exposures. The iTIE system was deployed to a depth of 3 m and evaluated in streams and marine harbors. Chemical analyses of water and iTIE chemical sorptive resins confirmed chemical groups causing lethal to sublethal responses. The system proved to be as sensitive or more so than the traditional phase 1 TIE test and required almost half of the resources to complete. This iTIE prototype provides a robust technology that improves stressor-causality linkages and thereby supports strong evidence for ecological risk weight-of-evidence assessments. Environ Toxicol Chem 2020;39:1746-1754. © 2020 SETAC.

Laboratory and Field-Based Assessment of the Effects of Sediment Capping Materials on Zinc Flux, Bioavailability, and Toxicity.

A former mining site has been the subject of extensive remediation and restoration, with a significant focus on disconnecting mine spoils from groundwater and managing the quantity and quality of runoff. A remaining task is ensuring concentrations of zinc (Zn) in the stream outflow of a pit lake are reduced below water quality standards. The efficacy of multiple capping materials for decreasing Zn dissolution from sediments was conducted under natural and reasonable worst-case conditions (pH = 5.5). Capping materials included AquaBlok™, limestone, and limestone-bone char. Field exposures were conducted in limnocorrals that isolated overlying water columns above the sediment and capping treatments. Simultaneous in situ and ex situ toxicity tests were conducted using Daphnia magna, Hyalella azteca, and Chironomus dilutus. In situ caged organisms were protected from temperature shock (warm epilimnetic waters) by deploying within a Toxicity Assessment Container System (TACS). Organisms were exposed to surficial sediments, caps, and hypolimnetic overlying waters for 4 d. Ex situ testing was conducted in core tube mesocosms containing sediments and caps at similar temperatures (15-19 °C). Results demonstrated the usefulness of TACS deployment in stratified lake systems. There were no differences in responses between treatments involving sediment capping materials in both in situ and ex situ tests. The lack of differences was likely due to dissolved Zn in surface water being below the hardness-adjusted threshold effects levels (164 µg L-1 ). This field- and laboratory-based weight-of-evidence study provided site-specific data to support the selection of an effective remedy, with reduced uncertainty compared to laboratory and chemistry-only approaches. Environ Toxicol Chem 2019;39:240-249. © 2019 SETAC.

Seasonal Toxicity Observed with Amphipods (Eohaustorius estuarius) at Paleta Creek, San Diego Bay, USA.

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10-d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition-associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229-239. © 2019 SETAC.

Hyporheic Interactions Increase Zinc Exposure and Effects on Hyalella azteca in Sediments under Flow-Through Conditions.

Groundwater-surface water interactions in the hyporheic transition zone can influence contaminant exposure to benthic macroinvertebrates. In streams, hyporheic flows are subject to varying redox conditions, which influence biogeochemical cycling and metal speciation. Despite these relationships, little is known about how these interactions influence the ecological risk of contaminants. The present study investigated the effects of hyporheic flows and zinc (Zn)-contaminated sediments on the amphipod Hyalella azteca. Hyporheic flows were manipulated in laboratory streams during 10-d experiments. Zinc toxicity was evaluated in freshly spiked and aged sediments. Hyporheic flows altered sediment and porewater geochemistry, oxidizing the sediments and causing changes to redox-sensitive endpoints. Amphipod survival was lowest in the Zn sediment exposures with hyporheic flows. In freshly spiked sediments, porewater Zn drove mortality, whereas in aged sediments simultaneously extracted metals (SEM) in excess of acid volatile sulfides (AVS) normalized by the fraction of organic carbon (fOC) [(SEM-AVS)/fOC] influenced amphipod responses. The results highlight the important role of hyporheic flows in determining Zn bioavailability to benthic organisms, information that can be important in ecological risk assessments. Environ Toxicol Chem 2019;38:2447-2458. © 2019 SETAC.

Metal Toxicity During Short-Term Sediment Resuspension and Redeposition in a Tropical Reservoir.

Billings Complex is the largest water-storage reservoir in São Paulo, Brazil, and has been contaminated since the 1960s. Periodically, Billings sediments are subjected to currents causing resuspension and subsequent release of metals. A short-term (4-h) resuspension was simulated using sediment flux exposure chambers (SeFECs) to better understand the fate, bioavailability, and transport of iron (Fe), manganese (Mn), and zinc (Zn) during these events, as well as possible organism toxicity. Daphnia magna and Hyalella azteca were exposed during the 4-h resuspension, and were monitored after exposure for survival, growth, and reproduction. Resuspension rapidly deoxygenated the overlying water, decreased the pH, and resulted in elevated dissolved Zn above the US Environmental Protection Agency's (2002) criteria for acute toxicity (120 µg L-1 ). However, Zn was scavenged (after 20 h) from solution as new sorption sites formed. Dissolved Mn increased during and after resuspension, with maximum values at 20 h post exposure. An initial release of Fe occurred, likely associated with oxidation of acid-volatile sulfides, but decreased after 1 h of resuspension. The Fe decrease is likely due to precipitation as oxyhydroxides. No acute toxicity was observed during resuspension; however, mortality of D. magna and H. azteca occurred during the postexposure period. Daphnia magna also exhibited chronic toxicity, with decreased neonate production after exposure. This sublethal effect could lead to decreased zooplankton populations over a longer period in the reservoir. Environ Toxicol Chem 2019;38:1476-1485. © 2019 SETAC.

Thermal extremes can intensify chemical toxicity to freshwater organisms and hence exacerbate their impact to the biological community.

Temperature in freshwater ecosystems fluctuates daily, seasonally and yearly. Climate change further induces temperature variations. In this study, we hypothesise that water temperatures, in particular thermal extremes, can significantly influence chemical toxicity to ectothermic organisms. Although temperature-dependent chemical toxicity (TDCT) is a classic research area in ecotoxicology, a unified model for predicting TDCT for freshwater species is yet to be developed. This study aimed to address this challenging issue through a meta-analysis by comparing acute toxicity endpoints (i.e. median lethal or effective concentration data; LC50 or EC50) of 13 chemicals for various freshwater species generated from different temperatures. Our results suggest that in most cases, freshwater species exhibit the highest tolerance towards chemicals at their physical optimal temperature (Topt), and chemical toxicity exacerbates when temperature is higher or lower than Topt (i.e. inverted V-shaped model between temperature and LC50 or EC50). Such observations are further supported by temperature-dependent hazardous concentration 10% (HC10) values derived from species sensitivity distributions constructed using toxicity data generated at different temperatures. A unified mathematical model was also developed to describe the inverted V-shape relationship between temperature and HC10 derivations. Overall, considering the natural variations of freshwater temperatures, the inverted V-shaped TDCT model can be readily applied to derive water quality guidelines and assess ecological risks of chemical contaminants.

Human Health Benefits from Fish Consumption vs. Risks from Inhalation Exposures Associated with Contaminated Sediment Remediation: Dredging of the Hudson River.

BACKGROUND: Billions of dollars are spent on environmental dredging (ED) to remediate contaminated sediments, with one goal being reduced human health risks. However, ED may increase health risks in unanticipated ways, thus potentially reducing net benefits. OBJECTIVES: To assess the ways that ED may increase health risks in unanticipated ways, thus potentially reducing net benefits, we quantitatively assessed a subset of population health benefits and risks of ED, using the 2009-2015 remediation of the Hudson River Polychlorinated Biphenyls (PCBs) Superfund Site as a case study. Three remediation scenarios were evaluated: No Action (NA), Source Control (SC), and ED. METHODS: We quantified health benefits for each scenario from reduced PCB levels in Hudson River fish, and health risks from ED operations due to increased inhalation exposures to PCBs and fine particulate matter (PM2.5), using disability-adjusted life years (DALYs) as a common metric. Occupational health risks were also considered in a separate sensitivity analysis. Estimates of population-level benefits and risks included Monte Carlo simulation-based uncertainty analysis. RESULTS: Under NA, fish consumption would result in an estimated health burden of 112 DALYs, and ED would lead to a reduction of 15 DALYs in excess of SC. ED operations were estimated to induce a total burden of 33 DALYs, dominated by PM2.5 impacts from rail transport emissions (32 DALYs). Including uncertainty, the net health benefit of ED ranged from -138 to +1,326 avoided DALYs (90% confidence), with a median of -11 avoided DALYs. CONCLUSIONS: For the considered impacts, ED in the Hudson River might not have led to an overall net positive human health impact. The benefits and risks of ED, however, have different degrees of uncertainty and involve different populations. Reducing long-distance transport of dredged sediment is a priority. This comparative approach could be used prospectively to better determine trade-offs involved in different remediation scenarios and to improve remediation design to maximize benefits while minimizing risks. https://doi.org/10.1289/EHP5034.