Does Improving a Firm's Environmental Management System and Environmental Performance Result in a Higher Stock Price?

<h3>Abstract</h3> Organophosphorus pesticides (OPs) are a chemically diverse class of insecticides that inhibit acetylcholinesterase (AChE). Many OPs require bioactivation to their active oxon form via cytochrome P450 to effectively inhibit AChE. OP toxicity can be mitigated by detoxification reactions performed by carboxylesterase and paraoxonase. The relative extent of bioactivation to detoxification varies among individuals and between species, leading to differential susceptibility to OP toxicity. Because of these species differences, it is imperative to characterize OP metabolism in model systems used to assess OP toxicity to adequately evaluate potential human hazard. We have shown that the asexual freshwater planarian <i>Dugesia japonica</i> is a suitable model to assess OP neurotoxicity and developmental neurotoxicity via rapid, automated testing of adult and developing organisms in parallel using morphological and behavioral endpoints. <i>D. japonica</i> has two cholinesterase enzymes with intermediate properties between AChE and butyrylcholinesterase that are sensitive to OP inhibition. Here, we demonstrate that this planarian contains the major OP metabolic machinery to be a relevant model for OP neurotoxicity studies. Adult and regenerating <i>D. japonica</i> can bioactivate chlorpyrifos and diazinon into their respective oxons. Significant AChE inhibition was only observed after <i>in vivo</i> metabolic activation but not when the parent OPs were directly added to planarian homogenate. Additionally, we found that <i>D. japonica</i> has both carboxylesterase and paraoxonase activity. Using specific chemical inhibitors, we show that carboxylesterase activity is distinct from cholinesterase activity. Taken together, these results further support the use of <i>D. japonica</i> for OP toxicity studies.