Pesticides, chemical stability tests

Chemical Stability - The most critical test for an end-use product is chemical stability of the pesticide active ingredient. Evaluation of chemical stability does not depend on any particular property of a mineral carrier or solid diluent. Evaluations are carried out by asking whether active ingredient is stable in the end-use formulation for a certain length of time under certain storage conditions. Answering the question makes use only of a chemical analysis for active ingredient, and is essentially independent of any property of the mineral. 

The GLP requirements for mixtures with carrier (40 CFR 160.113) were originally intended to address problems associated with the incorporation of test and control substances into feed, water, and other media for toxicology studies however, now these same requirements pertain to all other GLP-required studies, including those pertaining to re-entry and worker safety. The requirement involves (1) substantiation of test, control, and reference substance concentration through periodic analyses (2) verification of homogeneity and (3) determination of stability and, if applicable, also solubility. All of these requirements usually require chemical analysis, although bioassay may be necessary for microbial pesticides. 

Woutersen et al. (1985, as cited in Kalberlah and Schneider 1998 ECETOC 1995, 2003) evaluated toxicity data relating to 82 substances including stabilizers, plasticizers, antioxidants, disinfectants, food additives, pesticides, other agrochemicals, and industrial chemicals. The substances were each tested (oral administration to rats) for a subacute (2-4 weeks) and a subchronic (13-18 weeks) duration of exposure. Both the NOAEL and the LOAEL were included in the comparison. For 56% of the substances (46), the ratio NOAELsubacute/ NOAELsubchronic was about 1. For 44% of the substances (36), the subchronic NOAEL was lower than the subacute NOAEL (i.e., the ratio was above 1), and for 3/82 substances, the ratio was above 100. The 95th percentile was about 10. A factor of 4 covered 70%-80% of the substances. 

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