Evaluation and Development of Aquatic Toxicity Test Methodologies

Abstract

International chemical management legislation such as the European Union's REACH (Registration, Evaluation, Authorisation, and Restriction of Chemicals) has increased the need for more and better toxicity data while recognizing the 3R's of animal use (reduction, replacement, and refinement). To address this need, the Organisation for Economic Cooperation and Development's (OECD) Fish Toxicity Framework guidance document recommended improvements to test guidelines and integrated testing strategies. This study contributes to recommendations outlined in the Fish Toxicity Framework and similar guidelines.

Chapter I introduces the Embryonic Developmental Rate Assay (EDRA), a streamlined approach that uses nonlethal endpoints to assess toxicity. Time-lapse video technology was used to track the timing of seven developmental stages covering embryogenesis through hatching. Embryos exposed to two known toxicants demonstrated that developmental timing and rate were effective biomarkers for toxicity.

Another refinement to test methodology is presented in Chapter II. The Stepwise Information-Filtering Tool (SIFT) is a systematic method to break down large toxicity datasets for analysis in a stepwise manner, applying user-defined criteria to address reliability and relevance. A case study application of SIFT to analysis of a chronic daphnid toxicity dataset was presented, as well as a comparison to two similar data quality methodologies.

In Chapter III, the relationships between common summary statistics in toxicity testing were evaluated. The widely used hypothesis-based NOEC (No Observed Effect Concentration) has critical issues (e.g., impact of test design, no confidence levels). The ECx (Effect Concentration, with x as the percentage effect compared to controls) is regression-based, where x at a low percentage (e.g.10 or 20%) is considered an analogue to the NOEC. Using a chronic daphnid toxicity dataset, the relationship of NOEC to EC10 and EC20 and the impact of test parameters to the relationship was evaluated.

Threshold of toxicological concern (TTC) concepts have been used for years to estimate `safe' concentrations for low-volume chemicals or additives, although this concept has not yet translated to ecotoxicological thresholds (ecoTTC). In Chapter IV, a comprehensive dataset was constructed, analyzed for ecoTTC values, and evaluated for the influence of chemical class, endpoint selection, and regional application factor choice.