Alachlor toxicity

Howe, G.E., R. Gillis, and R.C. Mowbray. 1998. Effect of chemical synergy and larval stage on the toxicity of atrazine and alachlor to amphibian larvae. Environ. Toxicol. Chem. 17 519-525. 

The herbicide alachlor (4.146, Fig. 4.7) also displayed species-dependent toxicity, since it induced nasal tumors in rats but not in mice. Its metabolic scheme in rats and mice (Fig. 4.7) shows that alachlor can be transformed into 2,6-diethylaniline (4.149) by two different pathways, one of which proceeds via formation of 4.147. The other pathway implies glutathione (GSH) conjugation, followed by /3-lyase-mediated liberation of the thiol, followed by S-methylation to produce the methylsulfide 4.148. The two secondary amides 4.147 and 4.148 were hydrolyzed by microsomal arylamidases, but alachlor itself was not a substrate for this enzyme. The hydrolytic product 2,6-diethylaniline (4.149) was oxidized in nasal tissues to the electrophilic quinonimine metabolite 4.150, which can bind covalently to proteins. Aryl-... 

U.S. Environmental Protection Agency, Pesticide Fact Sheet Number 97.1 Alachlor, Office of Pesticides and Toxic Substances, Washington, DC, 10-63, 1987. 

Bipyridyl herbicides include alachlor, amitrole, atrazine, bromacil, bromoxynil, butylate, cyanazine, dalapon, dicamba, diuron, linuron, fluometuron, hexazinone, molinate, metolachlor, oryzalin, pendimethalin pronamide, propanil, propazine, simazine, terbacil, triallate, and triclopyr. In addition to these herbicides, the most common bipyridyls are diquat and paraquat. Paraquat is more toxic than diquat and produces chronic abnormal cell growth in the lungs, cornea and lens of the eye, nasal mucosa, skin, and fingernails. Diquat affects the eye lens and intestinal tract lining, but does not usually produce the frequently fatal lung changes characteristic of paraquat. 

No specific information on the acute toxicity of alachlor in humans is available. 

However, a 6-month dog study showed liver toxicity at all doses above 5 mg kg May and a 1-year study established that above lmgkg day alachlor causes effects in the liver, spleen, and kidney. In 2-year rat studies, doses above 2.5 mg kg day caused irreversible degeneration of the iris and related eye structures. 

Alachlor is moderately toxic to fish. The bioaccumulation factor in the channel catfish is 5.8 times the ambient water concentration, indicating that alachlor is not expected to accumulate appreciably in aquatic organisms. It is phytotoxic to sugar beet and cucurbits. The Material Safety Data Sheet should always be referred to for detailed information on handling and disposal. 

The first synthetic herbicide12 was 2,4-dichlorophenoxy-acetic acid (11.7). The one used in largest volume today is atrazine, which is typical of a group of triazine herbicides. Glyphosate (very low mammalian toxicity) is used extensively to kill vegetation nonselectively.13 Alachlor is a typ-... 

Alachlor does not appear to be highly toxic on an acute basis. The oral LD50 value for rats was reported to be 930 mg/kg and the dermal LD50 was 13,300 mg/kg in rabbits. 

The activity of soil dehydrogenase at the beginning of the soil dilution experiment in 0, 10, 50, and 90% diluted waste-pile soil was 18, 0, 65, and 138%, respectively, of the activity in CHECK soil. After 21 days, soil dehydrogenase was still inhibited in the 0 and 10% diluted waste-pile soil. The inhibition of enzyme activity suggests that high concentrations of alachlor may be toxic, but microbial bioactivity can be restored if contaminated soil is diluted enough. 

Alachlor is virtually nontoxic to mammals, its acute oral ld, for rats being 1800 mg/kg, and lDjq for pheasants 10 000 mg/kg. It is toxic to Osh, the lCj (96 hour exposure) for rainbow trout being 2.3 ppm, for bluegill 13.4 ppm. 

Guideline values proposed by the World Health Organization based on a toxicological approach for each substance are 2 /rg/l for simazine and atrazine, and 20 /rg/l for alachlor. Directive 91/414/CE harmonizes at the European scale the principle of authorization delivery of active substances. For example, a herbicide can be introduced in the positive list of the directive Annex 1 if only the scenario takes into account toxicity, ecotoxicity, and study on presence and fate in the environment, in order to exclude aU risks of groundwater contamination at levels higher than... 

Very little information is available on the toxic effects of alachlor in animals or humans. The oral LD50 value in mice is 462 mg/kg (NIOSH 1986). The dermal toxicity is very low in rabbits. It tested positive in a S. cerevisiae gene conversion test for mutagenicity. 

Toxic Categories Paraquat (Restricted Use) Metolachlor (Moderately) and Alachlor (Slightly). ... 

Kross, B.C. Vergara, A. Raue, L.E. Toxicity assessment of atrazine, alachlor, and carbofuran and their respecive environmental metabolites using Microtox. J. Toxicol Environ Heath. 1992. 37,149-159. 

New herbicides continue to be introduced. Resolve Q is an herbicide for use on corn, which contains rimsulfuron, 24.10 thifensulfuron, 24.11 and isoxadifen ethyl, 24.12.24.10 and 24.11 are part of a new family of environmentally compatible sulfonyl urea herbicides, which target the acetolactate synthase enzyme. Alachlor, 24.13, is used for grasses and broad-leaved weeds in corn, soya, and peanuts but is banned in the EU because of its toxicity. Mesotrione, 24.14, based on a substance isolated from the Californian bottlebrush plant, is more generally accepted and can be applied both pre- and postemergence it inhibits the plant enzyme 4-hydroxyphenylpyruvate dioxygenase. 

---