report no. 1/14
The Target Lipid Model (TLM) provides a framework for deriving predicted no effectconcentrations (PNEC) for nonpolar organic chemicals to organisms in theenvironment. This approach has been used to perform environmental riskassessment of individual hydrocarbons as well as complex petroleum substances.The TLM is based primarily on data for aquatic test organisms and this work evaluatesthe potential for extending the TLM to soil and sediment using Equilibrium Partitioning(EqP) theory.Literature data for other nonpolar organics were compiled for acute and chronicexposures to invertebrates in soils and sediments. New data were generatedaccording to OECD guidelines (CONCAWE, 2011 and 2012) to evaluate soil andsediment dwelling organisms and to test potential toxicity cut-offs for high log Kowcompounds. The default TLM was applied to these data using EqP to develop criticaltarget lipid body burdens (CTLBB) including associated uncertainty in the modelapplication.Comparison of the CTLBBs for soil and sediment species to CTLBBs from the largerTLM database for aquatic organisms showed little difference in the relative sensitivitybetween these two groups of species within the uncertainty of the model andexperimental data. Furthermore, the acute to chronic ratios (ACRs) for soil andsediment tests were within the range of ACRs for aquatic organisms exposed tononpolar organic chemicals.The TLM-derived PNEC applied to these data, also, demonstrated sufficient level ofprotection approximately 95% of data above PNEC, even for chemicals up tolog Kow 6. For chemicals with log Kow >6 an increasing incidence of no observedtoxicity consistent with the dataset for aquatic organisms was observed. The durationof the pre-equilibration step was important for some chemicals. For example, toxicitywas observed for these chemicals following short pre-equilibration times (whereas no toxicity was observed for spiked soils that had been aged up to 7 weeks prior to exposure.In conclusion, the work shows that the TLM can be extended to the soil and sedimentcompartments using the EqP for the purposes of a tier 1 risk assessment.