The measurement and induction of mixed function oxyigenases (MFOs) of limnetic gastropods were investigated to estimate their suitability as biomarkers. A determination of MFO activities was performed through the measurement of ethoxyresorufin-O-dealkylase (EROD), pentoxy-(PROD) and benzoxyresorufin-O-dealkylase-activity (BROD). Optimal measuring conditions of these activities were investigated in preparations of the digestive gland of 4 species of limnetic gastropods. Results indicate that MFO-activity inhibiting substances are accumulating in the microsomal pellet, the fraction commonly used for the measurement of MFO-activities. Therefore, the fraction used for induction studies was the postmitochondrial supernatant (PMS). EROD, PROD, and BROD activity ofPlanorbis planorbis andPlanorbis carinatus were measured after a treatment with Aroclor 1254 for 1–17 days. Maximal induction of EROD and PROD were 6 and 10 times the value in the control group ofP. carinatus, respectively induction inP. planorbis was lower. BROD-activity could not been measured inP. planorbis. InP. carinatus, BROD-activity increased to a maximum of 2 times after traetment with Aroclor 1254. The level of induction of EROD-activity is comparable to results described in analog studies with fish.

The effects of environmental policy on trade and social welfare are analyzed in a modified Heckscher-Ohlin framework where pollution is embodied in a good consumed. Utility is non-homothetic to account for changes in the demand for healthy goods when income increases. If the polluting input is used intensively, taxing it alone can cause an increase in the good's level of pollution concentration. Instead, a tax on the polluting input in combination with a subsidy to the non-polluting input can result in Pareto improvement. Contrary to other approaches, an abatement policy does not necessarily have a negative effect on a country's comparative advantage. However, if the country is large, change in terms of trade may cause one country to be made better off at the expense of the other, which suggests that compensatory payments may be required to encourage abatement policies.