A new screening index for pesticides leachability to groundwater.

Given the fact that pesticides exist in the aquatic environment at very low concentrations, it is clear that their analysis require expensive analytical techniques. Water authorities in Turkey are in need of assessing the likelihood of pesticide occurrence in groundwater in order to identify minimum number of pesticides that would be included in monitoring programs. To this purpose, the pesticides used in Turkey are ranked and those having higher leaching potentials are identified using pesticide screening leaching indexes. A total of 15 indexes (AF, AFR/AFT, Hamaker's RF, Briggs's RF, LPI, VI, LIX, GUS, Hornsby, LEACH, MLEACH, PLP, GWCP, LIN and GLI) was adopted and leaching potentials of 157 pesticides used in Turkey were estimated. Because each index is based on different pesticide/soil characteristics, each produced a different ranking. In order to emphasize variation in rankings and bring out a strong pattern, the statistical technique of Principal Component Analysis was used and a new composite index named as "YASGEP-P" was developed, the most relevant components (indices) were identified and the corresponding factor scores were calculated. This new index came out as a composite of GUS, LIX, MLEACH, LIN, Briggs's RF, Hamaker's RF, PLP and AFR indices. It was seen that all these indices except AFR are almost equally dominant and increase the value of YASGEP-P index, whereas AFR is also dominant but causes a decrease in YASGEP-P index value. The new index developed tends to discriminate between the relatively more soluble/less sorbable and more sorbable/less soluble pesticides. With the use of this composite index, the pesticides used in Turkey were sorted from the most leachable to least leachable and the priority pesticides to be monitored in the groundwaters were identified.