The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
Alachlor was selected for evaluation as a sensitizing agent for contact hypersensitivity in mice. ALAC is a pre-emergence and early post-emergent herbicide used against annual grasses and many broadleafed weeds. Alachlor has been shown to cause tumors in laboratory animals during chronic studies. Repeated contact with alachlor may cause an allergic skin reaction. It has also been reported to cause eye irritation. Studies with the rabbit have indicated it to be practically nonirritating to the eye and slightly irritating to the skin. Skin allergy was observed in guinea pigs following repeated skin exposure (Monsanto Material Safety Data). No reference in the literature could be found that indicated the compound was tested in mice.
The objective of this study was to determine the sensitizing potential of alachlor when applied dermally to female B6C3F1 mice.
Alachlor was tested on female B6C3F1 mice. The doses of alachlor ranged from 0.3% to 3.0% in acetone (99.5%) for sensitization, and 3.0% for challenge. Mice received 20 µl by direct dermal application for 5 consecutive days to a prepared site . Site preparation included intradermal injection of Freund's complete adjuvant in some mice (1-fluoro-2,4-dinitrobenzene, 98.6%, Sigma Chemical Co.) was used as the positive control at a concentration of 0.25% for sensitization, and 0.5% for challenge. Measurement of the contact hypersensitivity response was accomplished by the Mouse Ear Swelling Test, and the local lymph node assay.
The MEST indicated that alachlor was a sensitizer. A statistically significant (p<0.05) response was observed with 3.0% alachlor. The response was observed on the second day, but not on the first dayfollowing challenge, and was only observed in animals pretreated with Freund's complete adjuvant.
The LLNA, with no irritancy control, and using either dissociated cells or solubilized lymph nodes,detected a significant response (p<0.01) with 3.0% alachlor. The method, using solubilized lymphnodes, also detected a significant response (p<0.01) using 1.0% alachlor. However only the 3.0% concentration yielded cpm greater than three times the vehicle value, the recommended minimum difference indicative of a sensitizer (Kimber et al., Toxicology Letters. 55: 203-213, 1991). The local lymph node assay incorporating an irritancy control also detected a significant response with 3.0% alachlor (1.0% was not tested).