Anita H. Poulsen

Benchmarking Organic Micropollutants in Wastewater, Recycled Water and Drinking Water with In Vitro Bioassays

Thousands of organic micropollutants and their transformation products occur in water. Although often present at low concentrations, individual compounds contribute to mixture effects. Cell-based bioassays that target health-relevant biological endpoints may therefore complement chemical analysis for water quality assessment. The objective of this study was to evaluate cell-based bioassays for their suitability to benchmark water quality and to assess efficacy of water treatment processes. The selected bioassays cover relevant steps in the toxicity pathways including induction of xenobiotic metabolism, specific and reactive modes of toxic action, activation of adaptive stress response pathways and system responses. Twenty laboratories applied 103 unique in vitro bioassays to a common set of 10 water samples collected in Australia, including wastewater treatment plant effluent, two types of recycled water (reverse osmosis and ozonation/activated carbon filtration), stormwater, surface water, and drinking water. Sixty-five bioassays (63%) showed positive results in at least one sample, typically in wastewater treatment plant effluent, and only five (5%) were positive in the control (ultrapure water). Each water type had a characteristic bioanalytical profile with particular groups of toxicity pathways either consistently responsive or not responsive across test systems. The most responsive health-relevant endpoints were related to xenobiotic metabolism (pregnane X and aryl hydrocarbon receptors), hormone-mediated modes of action (mainly related to the estrogen, glucocorticoid, and antiandrogen activities), reactive modes of action (genotoxicity) and adaptive stress response pathway (oxidative stress response). This study has demonstrated that selected cell-based bioassays are suitable to benchmark water quality and it is recommended to use a purpose-tailored panel of bioassays for routine monitoring.

Methods for Deriving Pesticide Aquatic Life Criteria for Sediments

In this review, we evaluated three main current approaches for deriving sediment quality guidelines: empirical, mechanistic (equilibrium partitioning), and spiked sediment toxicity testing approaches. Empirical approaches determine ranges of sediment concentrations that are likely or unlikely to cause toxicity, based on large datasets of matching sediment chemistry, field, and laboratory toxicity data. The empirical approaches are not suitable for determining SQC for specific pesticides because (I) direct cause-effect relationships between single sediment contaminants and toxicity cannot be discerned; (2) chemistry measurements have not accounted for bioavailability, which leads to numeric values with high uncertainty and low reliability; and (3) for many pesticides, little or no matching chemistry and toxicity data are available. In the EqP approach, SQC are derived by entering existing aquatic toxicity data into the equilibrium-partitioning model. This approach is practical for pesticides with water quality criteria in place, but the assumption of equilibrium in aquatic ecosystems is questionable, and the EqP approach neglects available sediment toxicity data. The SSTT approaches utilize sediment toxicity data, creating a scientifically defensible foundation for SQC, but experimental uncertainties regarding spiking technique and equilibration times are yet to be eliminated. The species sensitivity distribution approach generates criteria with confidence intervals, providing a measure of uncertainty, but requires relatively large datasets, whereas the assessment factor method lacks quantification of uncertainty but only requires few data to calculate conservative criteria. Several existing methodologies incorporate a combination of approaches that is dependent on data availability and the physicochemical properties of the compound of interest.A summary of the differences and similarities between key elements of the seven methodologies emphasized in this review is displayed in Table 6. One important element regarding sediment contamination is the incorporation of bioavailability and multiple exposure routes, which must be addressed to achieve a technically defensible methodology. It is crucial that bioavailability be incorporated in both criteria derivation and compliance determination (sampling) to ensure that data are comparable. Recent research on bioavailability of sediment contaminants has indicated that the freely dissolved pore water fraction corresponds well with uptake and toxicity. For species having significant exposure via ingestion of contaminated food and/or sediments and/or direct sediment contact, exposure may be underpredicted if these additional exposure routes are overlooked. Future SQC methodologies will be greatly improved by accounting for factors relevant for bioavailability and exposure pathways. To develop a completely new methodology, existing methodologies offer valuable building blocks that are well suited for adaptation. A new method will be more reliable and robust if it utilizes more refined risk assessments than currently are available in existing methodologies. To date, the most comprehensive methodologies for deriving single numeric SQC are those of the Netherlands and the EU,which include both SSTT and EqP approaches.