FROM PARTITION COEFFICIENTS TO MEDIAN LETHAL CONCENTRATION OF ORGANIC POLLUTANTS: EVALUATION OF PASSIVE SAMPLERS AS PROXY OF LIPID IN THE TARGET MODELS FOR FISH AND DAPHNIA

Abstract

The number and volume of chemicals around us have increased significantly since industrialization. The main challenge in ecotoxicity is to accurately identify and distinguish the risks of tens of thousands of chemicals on aquatic life. We put forward a new approach to estimate median lethal concentrations (LC50) of organic compounds by establishing target passive sampler models. In this study, we demonstrated that passive samplers are good proxies for the bio-membranes in organisms. Hence, passive samplers can be substituted in the target lipid model to predict the reliable baseline toxicities of chemicals accumulated on passive samplers. Our new approach sheds light on the mode of toxic actions of organic chemicals. We evaluated and categorized four types of passive samplers viz., polyacrylic (PA), polyethylene (PE), polydimethylsiloxane (PDMS) and polyoxymethylene (POM). The analyses showed that PA works well for most of the chemical groups such as baseline compounds. However, for a few chemical groups such as aldehydes and alpha, beta unsaturated ketones, the PDMS displayed a good agreement between estimated and experimental values. Our approach worked well for fish but showed significant systematic deviations from experimental values for daphnia. Further investigation indicated that the assumption of a critical burden of 100 mmol/kg in bio-membrane is suitable for fish but needs to be revisited for daphnia. The predictive performance of our new approach is at par with previous approaches. However, our method is simple and offers the opportunity of interfacing the measurement of environmental levels of organic pollutants with modeling of LC50 values of those chemicals.