Collection and use of porewater data from sediment bioassay studies for understanding exposure to bioavailable metals.

The US Environmental Protection Agency Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel, Silver and Zinc) equilibrium partitioning approach causally link metal concentrations and toxicological effects; they apply to sediment and porewater (i.e., interstitial water). The evaluation of bioavailable metal concentrations in porewater, using tools such as the biotic ligand model, provides an advancement that complements sediment-based evaluations. However, porewater characterization is less commonly performed in sediment bioassays than sediment chemistry characterization due to the difficulty and expense of porewater collection as well as concerns about interpretation of porewater data. This study discusses the advantages and disadvantages of different porewater extraction methods for analysis of metals and bioavailability parameters during laboratory sediment bioassays, with a focus on peepers and centrifugation. The purpose is to provide recommendations to generate bioassay porewater data of sufficient quality for use in risk-based decision-making, such as for regulated cleanup actions. Comparisons of paired data from previous bioassay studies indicate that metal porewater concentrations collected via centrifugation tend to be higher than those collected via peepers. However, centrifugation disrupts the redox status of the sediment; also, metal concentrations can vary markedly based on centrifugation conditions. Data to compare the concentrations of peeper- and centrifugation-collected bioavailability parameters (e.g., major ions, pH) are much more limited, but indicate smaller differences than those observed for metal concentrations. While peepers can be sampled without altering the redox status of the porewater, the small volume of porewater peepers collected is enough for metal concentration analysis, but insufficient for analysis of all metal bioavailability parameters. Given the benefits of metal collection via peepers, it is optimal to use centrifugation and peepers in tandem for bioassay porewater collection to improve bioavailability predictions. Environ Assess Manag 2022;18:1321-1334. © 2021 SETAC.

Sediment toxicity data and excess simultaneously extracted metals from field-collected samples: Comparison to United States Environmental Protection Agency benchmarks.

US Environmental Protection Agency (USEPA) Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Metal Mixtures are based on the principle that metals toxicity to benthic organisms is determined by bioavailable metals concentrations in porewater. One ESB is based on the difference between simultaneously extracted metal (SEM) and acid volatile sulfide (AVS) concentrations in sediment (excess SEM). The excess SEM ESBs include a lower uncertainty bound, below which most samples (95%) are expected to be "nontoxic" (defined as a bioassay mortality rate ≤24%), and an upper uncertainty bound, above which most samples (95%) are expected to be "toxic" (defined as a mortality rate >24%). Samples that fall between the upper and lower bounds are classified as "uncertain." Excess SEM ESBs can, in principle, be improved by normalizing for organic carbon (OC). OC is a binding phase that reduces metals bioavailability. OC normalization should improve the accuracy of bioavailable metal concentration estimates, thus tightening uncertainty bounds. We evaluated field-collected sediments from 13 studies with excess SEM, OC, and bioassay data (n = 740). Use of the OC-normalized excess SEM benchmarks did not improve prediction accuracy. The ESB model predicts OC-normalized excess SEM exceeding the upper benchmark even when toxicity is not observed, because error in the OC normalization model increases at low OC concentrations. To minimize the likelihood of incorrectly identifying nontoxic samples as toxic, we recommend that OC normalization of excess SEM should not be considered for sediments with an OC concentration <1% and is questionable for sediments with an OC concentration of 1%-4%. Additional focused studies are needed to confirm or refine the minimum sediment OC concentrations that are applicable for reducing uncertainty in toxicity predictions due to excess SEM. Integr Environ Assess Manag 2022;18:174-186. © 2021 SETAC.

Refining our understanding of metal bioavailability in sediments using information from porewater: Application of a multimetal biotic ligand model as an extension of the equilibrium partitioning sediment benchmarks.

The equilibrium partitioning sediment benchmarks (ESBs) derived by the US Environmental Protection Agency (USEPA) in 2005 provide a mechanistic framework for understanding metal bioavailability in sediments by considering equilibrium partitioning (EqP) theory, which predicts that metal bioavailability in sediments is determined largely by partitioning to sediment particles. Factors that favor the partitioning of metals to sediment particles, such as the presence of acid volatile sulfide (AVS) and sediment organic matter, reduce metal bioavailability to benthic organisms. Because ESBs link metal bioavailability to partitioning to particles, they also predict that measuring metals in porewater can lead to a more accurate assessment of bioavailability and toxicity to benthic organisms. At the time of their development, sediment ESBs based on the analysis of porewater metal concentrations were limited to comparison with hardness-dependent metals criteria for the calculation of interstitial water benchmark units (IWBUs). However, the multimetal biotic ligand model (mBLM) provides a more comprehensive assessment of porewater metal concentrations, because it considers factors in addition to hardness, such as pH and dissolved organic carbon, and allows for interactions between metals. To evaluate the utility of the various sediment and porewater ESBs, four Hyalella azteca bioassay studies were identified that included sediment and porewater measurements of metals and porewater bioavailability parameters. Evaluations of excess simultaneously extracted metals, IWBUs, and mBLM toxic units (TUs) were compared among the bioassay studies. For porewater, IWBUs and mBLM TUs were calculated using porewater metal concentrations from samples collected using centrifugation and peepers. The percentage of correct predictions of toxicity was calculated for each benchmark comparison. The mBLM-based assessment using peeper data provided the most accurate predictions for the greatest number of samples among the evaluation methods considered. This evaluation demonstrates the value of porewater-based evaluations in conjunction with sediment chemistry in understanding toxicity observed in bioassay studies. Integr Environ Assess Manag 2022;18:1335-1347. © 2021 SETAC.

Framing scientific analyses for risk management of environmental hazards by communities: case studies with seafood safety issues.

Risk management provides a context for addressing environmental health hazards. Critical to this approach is the identification of key opportunities for participation. We applied a framework based on the National Research Council's (NRC) analytic-deliberative risk management dialogue model that illustrates two main iterative processes: informing and framing. The informing process involves conveying information from analyses of risk issues, often scientific, to all parties so they can participate in deliberation. In the framing process, ideas and concerns from stakeholder deliberations help determine what and how scientific analyses will be carried out. There are few activities through which affected parties can convey their ideas from deliberative processes for framing scientific analyses. The absence of participation results in one-way communication. The analytic-deliberative dialogue, as envisioned by the NRC and promoted by the National Institute of Environmental Health Sciences (NIEHS), underscores the importance of two-way communication. In this article we present case studies of three groups--an Asian and Pacific Islander community coalition and two Native American Tribes--active in framing scientific analyses of health risks related to contaminated seafood. Contacts with these organizations were established or enhanced through a regional NIEHS town meeting. The reasons for concern, participation, approaches, and funding sources were different for each group. Benefits from their activities include increased community involvement and ownership, better focusing of analytical processes, and improved accuracy and appropriateness of risk management. These examples present a spectrum of options for increasing community involvement in framing analyses and highlight the need for increased support of such activities.

Modeling developmental processes in animals: applications in neurodevelopmental toxicology.

Biologically based dose-response models can provide a framework for incorporating mechanistic information into our assessments of neurotoxicity considering both kinetic and dynamic processes. We have constructed models for normal midbrain and neocortex development and we have extended these models to evaluate the neurodevelopmental toxicity of ethanol and methyl mercury. Using such modeling approaches, we have been able to test hypothesized modes of action for these neurodevelopmental toxicants. Specifically, we have compared ethanol's effects on neocortical neurogenesis and exacerbation of apoptosis during the synaptogenesis period. We have used methylmercury as an example of how one can link toxicokinetic and toxicodynamic models and also as an example of how mechanistic data on gene expression can support model development. In summary, using examples from our research group, this paper illustrates the need for models that evaluate both qualitative and quantitative kinetic and dynamic factors in order to understand the potential impacts of neurodevelopmental toxicants.

A model for optimization of biomarker testing frequency to minimize disease and cost: example of beryllium sensitization testing.

A common problem with medical surveillance programs using biomarkers is determining the optimal frequency of testing to minimize adverse health effects and cost. In the case of beryllium-exposed workers, frequency of testing for beryllium sensitization may be especially important. Recent studies indicate a lack of dose response for beryllium sensitization, but do support a dose response for the development of chronic beryllium disease (CBD). Though unproven, this implies that early identification of sensitization and immediate removal from exposure may reduce development of CBD. A model is proposed to project the optimal frequency of sensitization testing using the current beryllium lymphocyte proliferation test (BeLPT) to minimize disease-related costs, assuming that a positive BeLPT will precede CBD. Conversion rates for cumulative exposure to disease development were adapted from the literature and used with testing costs and cost of disease estimates in the model. The model was run assuming several test frequency regimes. Results support the use of periodic testing in line with the annual schedule proposed in the Final Chronic Beryllium Disease Prevention Program Rule (1999) following initial testing within three months of first beryllium exposure. The financial and health benefits of reducing the time from exposure to detection of early disease was also explored with the model and demonstrated as a highly desirable characteristic for an alternative test or improved BeLPT. Limitations of the approach are discussed as well as options for adapting this biomarker optimization methodology to consider biomarkers of other exposure-associated diseases.