Determining Pesticide Persistence on Plastic Mulches used as Row Covers in Tennessee

During the past decade, the use of plasticulture production systems has become an increasingly common practice for vegetable production in the United States. The plasticulture system is the use of plastic mulch to serve as a row cover in the field. The semi-permeable material can be made of varying densities of polyethylene, and serves as a barrier that helps maintain soil moisture and reduce weed growth. Increased use of these plastics has created a waste management problem, as producers have difficulties trying to find the best and cheapest disposal method. A few companies had begun collecting the materials for reprocessing and later reuse, but have shown reluctance due to the quantity of soil residues and possible chemical contamination.

The main goal of this research was to determine if chemical residues from earlier pesticide applications remain on the plastic at the end of the growing season. A laboratory method was developed so that the pieces of plastic could be measured for possible pesticide residue presence. Five commonly used pesticides in Tennessee were chosen as subject chemicals. The products used for research were: Sencor (metribuzin), Bravo (chlorothalonil), Quadris (azoxystrobin), Asana (esfenvalerate), and Thiodan (endosulfan. Laboratory methodologies using a new extraction technique and High Performance Liquid Chromatography (HPLC) to perform analytical measurements were developed and tested to allow all five chemicals to be measured in one procedure. The methods proved to work well, with extraction efficiencies greater than 89% and detection limits in the range of 10-112 ppb.

A field study was then conducted to measure the persistence of these pesticide residues on the plastic at the end of the growing season. A tomato production field typical of those found in Eastern Tennessee was prepared at the University of Tennessee Knoxville Experiment Station near Knoxville, Tennessee. The subject chemicals were applied according to rates recommended by the University of Tennessee Agricultural Extension Service. One square foot samples of plastic were collected after the final tomato harvest and were analyzed using the developed method. Results of the field experiment showed that the average amount of each chemical on each sample was less than 0.01 mg/per square foot of plastic except for β-endosulfan, which was approximately 0.2 mg/per square foot of plastic. When compared to the theoretical amount applied per square foot of plastic, all of the remaining amounts were less than 1.0% except for esfenvalerate which was as much as 5.0%.