Should Transformation Products Change the Way We Manage Chemicals?

Abstract

When chemical pollutants enter the environment, they can undergo diverse transformation processes, forming a wide range of transformation products (TPs), some of them benign and others more harmful than their precursors. To date, the majority of TPs remain largely unrecognized and unregulated, particularly as TPs are generally not part of routine chemical risk or hazard assessment. Since many TPs formed from oxidative processes are more polar than their precursors, they may be especially relevant in the context of persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances, which are two new hazard classes that have recently been established on a European level. We highlight herein that as a result, TPs deserve more attention in research, chemicals regulation, and chemicals management. This perspective summarizes the main challenges preventing a better integration of TPs in these areas: (1) the lack of reliable high-throughput TP identification methods, (2) uncertainties in TP prediction, (3) inadequately considered TP formation during (advanced) water treatment, and (4) insufficient integration and harmonization of TPs in most regulatory frameworks. A way forward to tackle these challenges and integrate TPs into chemical management is proposed.

Keywords: Water management; advanced oxidation processes; emerging contaminants; nontarget screening; risk assessment.

Figure 1

a) Scatterplot of log Koc and median DT50 values for pesticides and pesticide TPs. All DT50 values were taken from enviPath (www.envipath.org; Package: EAWAG-SOIL). High-quality Koc data for all pesticides and 159 TPs were extracted from the pesticide properties database (http://sitem.herts.ac.uk/aeru/ppdb/), while Koc values for an additional 410 TPs were calculated with KOCWIN, EPI Suite. (b) Scatter plot of the lowest number of predicted or observed transformation steps required to reach the persistent TPs TFA (www.envipath.org; Package: TP predictions TFA (BBD, top 50)) or 1,2,4-triazole (Package: EAWAG-SOIL) and the percentage of carbon of the precursor still remaining in the TPs for their precursor compounds among the 317 pesticides in (a).

Figure 2

Proposed actions and interactions of researchers, industry, and regulation to facilitate a better integration of TPs into chemicals management.