A Review of Mechanistic Models for Predicting Adverse Effects in Sediment Toxicity Testing

Metals and PAHs in surface sediment and biological effects on the amphipod Corophium orientale and on embryos of the oyster Crassostrea gigas

Surface sediments of the Venice lagoon were monitored in 2008 and 2011-2018 to evaluate sediment chemistry (with focus on metals and PAHs) and their toxicity on target organisms. The large dataset resulting from these investigations is evaluated in this study with respect to spatial distribution and background concentrations, chemical patterns and relationships of investigated chemicals with biological effects observed on the amphipod Corophium orientale (exposed to sediments), and on embryos of the oyster Crassostrea gigas (exposed to elutriates). The evaluation is performed considering mechanistic sediment quality guidelines and, for elutriate, toxicity data available in scientific literature (EC50, Effective Concentrations derived single substance laboratory test). Although exceedance of the background concentrations defined in previous studies were observed for Zn, Cu, Pb, Cd and Hg (but not for As, Cr and Ni), tested sediments generally do not display relevant toxicity to C. orientale, whilst elutriates prepared from surface sediments can determine toxic effects on C. gigas, most likely due to the high level of ammonia. The concentrations of metals in elutriates generally appear lower than the EC50 reported in literature but their influence on C. gigas toxicity cannot be totally excluded. PAHs, evaluated on the basis of the TU approach, are not a stressor of main concern in the surface sediments investigated in the surveys. The results can support further evaluations aimed at sediment management actions in the Venice lagoon, as well as sediment assessment in other areas characterized by similar conditions.

Integrating ex situ biomimetic extraction analyses into contaminated sediment assessment and management decisions

This study evaluated a novel ex situ passive sampling biomimetic extraction (BE) method to estimate toxic potency in sediments. Gas chromatography with flame ionization detection (GC-FID) analysis of polydimethylsiloxane fibers equilibrated with field sediments was used to quantify bioavailable polyaromatic hydrocarbons (PAHs) and other unresolved, site-specific contaminant mixtures. This method is biomimetic because contaminants partition to the fiber based on hydrophobicity and abundance, and GC-FID quantification accounts for all constituents absorbed to the fiber that may contribute to toxicity. This measurement was compared with conventional approaches that rely on bulk sediment or porewater measurements of a targeted suite of PAHs. The specific objectives of the study were to (1) describe the BE method and explain measurement translation into toxic units (TUs); (2) report sediment BE data collected across 17 diverse field sites; (3) compare TUs predicted from (i) equilibrium partitioning (EqP) calculations based on sediment total organic carbon and bulk PAH chemistry, (ii) PAH porewater concentrations derived using ex situ passive sampling, and (iii) BE concentrations; and (4) discuss implications of this analysis for benthic toxicity assessment. Results showed that TUs obtained from EqP calculations were typically 10× higher than TUs derived from measured porewater PAH concentrations, indicating reduced PAH bioavailability in field sediments. Toxic units derived using the new BE method were more conservative than EqP in one-third of the sediments investigated, which was attributed to unquantified sediment contaminants, possible fiber fouling in the more contaminated sediments, and potential background interferences in less contaminated sediments. Preliminary data are also presented, showing that fluorometric analysis provides a simpler, promising alternative for estimating sediment BE concentrations. Based on this analysis, a decision-support framework is proposed using EqP and BE based TU metrics. Future research priorities are described for supporting framework implementation and extending use of BE analyses to remedial design and monitoring.

Sediment Toxicity Tests: A Critical Review of Their use in Environmental Regulations

Sediments are an integral component of aquatic systems, linking multiple water uses, functions, and services. Contamination of sediments by chemicals is a worldwide problem, with many jurisdictions trying to prevent future pollution (prospective) and manage existing contamination (retrospective). The present review assesses the implementation of sediment toxicity testing in environmental regulations globally. Currently, the incorporation of sediment toxicity testing in regulations is most common in the European Union (EU), North America, and Australasian regions, with some expansion in Asia and non-EU Europe. Employing sediment toxicity testing in prospective assessments (i.e., before chemicals are allowed on the market) is most advanced and harmonized with pesticides. In the retrospective assessment of environmental risks (i.e., chemicals already contaminating sediments), regulatory sediment toxicity testing practices are applied inconsistently on the global scale. International harmonization of sediment toxicity tests is considered an asset and has been successful through the widespread adoption and deployment of Organisation for Economic Co-operation and Development guidelines. On the other hand, retrospective sediment assessments benefit from incorporating regional species and protocols. Currently used toxicity testing species are diverse, with temperate species being applied most often, whereas test protocols are insufficiently flexible to appropriately address the range of environmental contaminants, including nanomaterials, highly hydrophobic contaminants, and ionized chemicals. The ever-increasing and -changing pressures placed on aquatic resources are a challenge for protection and management efforts, calling for continuous sediment toxicity test method improvement to insure effective use in regulatory frameworks. Future developments should focus on including more subtle and specific toxicity endpoints (e.g., incorporating bioavailability-based in vitro tests) and genomic techniques, extending sediment toxicity testing from single to multispecies approaches, and providing a better link with ecological protection goals. Environ Toxicol Chem 2024;43:1697-1716. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.