Statistical Ecotoxicological Modelling

Ecotoxicological risk assessment must be undertaken before a chemical can be deemed safe for application. The assessment is based on three components: hazard assessment, exposure assessment and risk characterisation. The latter is a combination of the former two. One standard approach is based on the deterministic comparison of exposure concentration estimates to the concentration of the toxicant below which adverse effects are unlikely to occur to the potentially exposed ecological assemblage. This concentration is known as the ‘predicted no effect concentration’ (PNEC).

At the level of hazard assessment we are concerned with, there is a requirement that procedures be straightforward and efficient, as well as being transparent. The PNEC is in general currently determined using either a fixed assessment factor applied to a summary statistic of observed laboratory derived toxicity data, or as a percentile of a distribution over the ecological community sensitivity. Often it is the situation that a hazard assessment will be based on substantially small samples of data.

In my research, I am interested in evaluating proposals for determining a PNEC according to regulatory guidance and scientific literature. In particular, my interests are:

  1. To explore methods under the context of alternative probabilistic models.

  2. The determination of conservative probabilistic estimators, which may be appropriate for lower-tier level risk assessment.

  3. Species non-exchangeability, a concept which is recognised by scientists and risk assessors, yet typically discounted in practice.

  4. Deriving novel PNECs that extend what is currently scientifically accepted, satisfy the requirements of being tractably straightforward to apply, and which are scientifically defensible.

  5. Assumptions of species sensitivity distributions (SSDs).