The Impact of Pesticides - Academy Publish

ecently explored on preliminary studies in vitro using trypsinized squamous cellcarcinoma, since they inhibit cellular metabolism including energy, protein, andnucleic acid metabolism, thereby, causing cell regression and death (Amanullah andHari, 2011).Three classes of carbamate compounds are known: i) the ester derivatives; ii) thosewith the general structure R 1 NHC(O)OR 2 , in which R1 and R2 are aromatic and/oraliphatic moieties, and iii) those containing a benzimidazole group (IPCS, 1986).In this chapter, the more relevant contributions, of the last ten years, to the currentknowledge on several aspects regarding carbamate pesticides, such as mode ofaction, effects on human health, legislation, monitoring, human exposure tocarbamate residues, risk and exposure assessment will be discussed.MODE OF ACTION AND TOXICOLOGYThe mechanism of carbamates poisoning, except herbicidal carbamates, involvescarbamylating of the active site of acetylcholinesterase leading to the inactivation ofthis essential enzyme which has an important role in nervous system of humans, andother animal species (Ecobichon, 2001). Carbamate compounds are often calledanticholinesterases. In the presence of inhibitors, acetylcholinesterase becomesprogressively inhibited and is not further capable of hydrolyzing acetylcholine tocholine and acetic acid (Jokanovic, 2009; Jokanovic and Maksimovic, 1997).Consequently, acetylcholine accumulates at cholinergic receptor sites and produceseffects equivalent to excessive stimulation of cholinergic receptors throughout thecentral and peripheral nervous system. Inhibited enzyme can be spontaneouslyreactivated, with reversal of inhibition occurring typically with half-time of an houror less after exposure (Jokanovic, 2009). This fact may reduce the possible period ofintoxication in situations of accidental overexposure or suicide attempts. Theinhibition of other esterases may also occur (Thompson, 1999).Herbicidal carbamates (such as carbetamide) which are a limited number ofcompounds are not inhibitors of cholinesterase and are cell division inhibitors(Tomlin, 1997). Plants can metabolize carbamates in which arylhydroxylation andconjugation, or hydrolytic breakdown are the main routes of detoxification. Theresults of a number of studies suggest that carbamates are exclusively distributed viathe apoplastic system in plants (IPCS, 1986).The acute toxicity of the different carbamates ranges from highly toxic to onlyslightly toxic or practically non-toxic (IPCS, 1986). Concerning the main carbamateinsecticides in use, their relative toxic potency estimated human values, (Erdman,2003) vary from high toxicity (LD 50 200 mg/kg; fenocarb, carbaryl, isoprocarb, MPMC(Meobal), MTMC (Metacrate, Tsumacide), XMC (Cosban)).AcademyPublish.org - The Impact of Pesticides22