Are PMOCs less toxic?

PMOCs require a distinct approach

The first day of the workshop was filled with interesting oral presentations about the challenges in the chemical analysis of PM compounds, their presence in the water cycle, and the applicability of current methods and regulations. Pim de Voogt made a presentation on PM compounds in drinking water treatment, while Thomas’s presentation addressed the question: Are persistent mobile organic compounds (PMOCs) less toxic than other organic compounds? The one question we hoped to answer during the workshop.

On the second day, the group split into break-outs to discuss various aspects of PMT compounds. Thomas led the break-out on ‘Toxicity and ecotoxicity of PM compounds’ and Astrid summarised the discussion on a flip-over.

The question whether PM compounds are less toxic than other organic compounds was hard to answer. Plant protection products for example, are designed to be persistent and toxic, but the toxicological mechanism is very specific. Knowledge about the mode of action of PM compounds is therefore very important. Members of the group had positive experiences with the use of bioassays on PM compounds and to a lesser extent with QSARs. It was also clear that the current hazard criteria are not applicable to PM compounds. Moreover, persistent compounds are present on a continuous basis, which means that the aquatic environment is chronically exposed to them, something that today’s ecotoxicology tests are not up to testing. A good interpretation of the results within yet-to-be-determined regulatory frameworks requires deeper insight into the toxicokinetics, intracellular and extracellular concentrations, and intrinsic potential of the target site of the substance. Mixture toxicity and effects in the field are general aspects that will also certainly be important for PM compounds. When more (toxicity) data become available, they can be added to a QSAR and contribute to defining an efficient testing strategy for PM compounds. In short: there’s still no answer to the one question. Setting up an expert group, publishing a position paper, and transforming ideas into research are the initial steps that will be taken in pursuit of an answer.