Pesticide-contaminated soil sample stability during frozen storage

Little information is available in the literature on pesticide-contaminated soil sample stability during frozen storage. This research was conducted t o evaluate the effects of sample holding times on frozen clay loam, clay, a nd loamy sand soils spiked with eight different herbicides: EPTC (S-ethyl d ipropylthiocarbamate); trifluralin (alpha, alpha, alpha-trifluoro-2,6-dinit or-N,N-dipropyl-p-toluidine); atrazine (6-chloro-N-2-ethyl-N-4-isopropyl-1, 3,5-triazine-2,4-diamine); alachlor (2-chloro-2',6'-diethyl-N-(methoxymethy l)acetanilide); dicamba (3,6-dichloro-2-methoxybenzoic acid); 2,4-D (2,4-di chlorophenoxyacetic acid); silvex ((+/-)-2-(2,4,5-trichlorophenoxy)propioni c acid); and 2,4,5-TB (4-(2,4,5-trichlorophenoxy)butanoic acid). Each soil was spiked with eight herbicides (1 mg kg(-1) each herbicide) and stored at -15 degrees C for up to 450 d. The pesticides tested could generally be st ored up to 450 d without affecting pesticide recovery on all soil types wit h the exception of trifluralin. Trifluralin decreased by 50% in the loamy s and, 40% in the clay loam, and 66% in the clay soil over the length of the study, In the loamy sand, clay loam, and clay soils a significant decrease in trifluralin concentration occurred at Day 180, 360, and 270, respectivel y. This study shows that long-term frozen storage can affect the sample int egrity of some pesticide-contaminated soils. In addition, soil type can be a factor in sample integrity during frozen storage. Spiked controls should be a part of quality assurance and quality control during long-term frozen storage.