Selection of priority properties to assess environmental hazard of pesticides

We assess the environmental hazard of 50 pesticides used in Italy by means of Hasse diagrams, a method based on graph theory. The criteria we use for ranking are persistence, and the physical-chemical properties, vapour pressure and water solubility, and yearly usage. When only the physical-chemical properties plus persistence are used to assess environmental hazard of pesticides in soils, eleven out of the 50 compounds studied here, methylbromide, bentazone, dalapon, diquat, linuron, mancozeb, metham-Na, TCA, metolachlor, paraquat, and simazine are considered potentially hazardous for the combination of long persistence in soil, high water solubility and low vapour pressure. Alachlor, atrazine, chloridazon, terbuthylazine and ziram are also a problem of concern because of their high loadings. To test whether the theoretical ranking is realistic, the list of identified compounds was compared with the results of monitoring studies carried out in the River Po. The assumption for this comparison is that, if the ranking method is correct, the probability of finding chemicals identified as hazardous should be higher than the probability of finding less hazardous chemicals. Chemicals ranked lower have less probability of being found both because of lower usage and because they are less persistent and/or less leachable. Results are quite encouraging since seven pesticides identified by our ranking method as most hazardous, alachlor, atrazine, bentazone, linuron, metolachlor, simazinc and terbuthylazine of the 8 analyzed for (previous plus TCA) were found, a success ratio of 88%. Results for all the other chemicals are presented in the paper. The second purpose of this study was the identification of the most important criteria to assess the chemicals; this assessment was performed using a matrix W. We concluded that the elimination of the criterion “usage” affects ranking more than the elimination of water solubility. However, none of the criteria, water solubility, vapour pressure, persistence and yearly usage can be eliminated, too much information would be lost if they were omitted. This conclusion is consistent with our decision to use only few criteria to rank the chemicals, criteria that are deemed to be independent of each other.