Chloropicrin:  Reactions with Biological Thiols and Metabolism in Mice

Abstract

Chloropicrin (CCl3NO2) is a preplant soil fumigant as a fungicide, warning agent for other fumigants, and former was gas. Its mode of action is unknown but presumably related to its facile metabolic dechlorination on reaction with biological thiols. These interactions were studied with 14CCl3NO2, 14CHCl2NO2, 14CH2ClNO2, and 14CH3NO2, synthesized for this purpose. Reaction of 14CCl3NO2 with GSH yields the di- and monochloro derivatives, GSSG, and a small amount of nitrite. The initial adduct with GSH is transient, but more stable derivatives are formed at longer times or on catalysis by GSH S-transferase. Human Hb, examined as a model thiol protein, reacts with 1.5 mol equiv of 14CCl3NO2 at pH 7.4 to produce 53-67% 14CHCl2NO2 and 10-11% Hb dducts (radiochemical yields) which, on longer incubation, release 14CHCl2NO2, CHCl2NO2 and CH2ClNO2 react with the same site(s) in Hb but more slowly. The dechlorination reactions are also catalyzed by liver cytosol and microsomes with NADPH. Dechlorination and adduct formation observed in vitro also occur in vivo in ip-treated mice. Thus, 14CCl3NO2 quickly gives 14CHCl2NO2, and some 14CO2 is formed, but the primary urinary metabolites are polar and nonvolatile. The major metabolite from 14CCl3NO2 in urine is less polar than those from 14CHCl2NO2, 14CH2ClNO2, and 14CH3NO2 which, in turn, are different from the 14CH2O and H14CO2Na metabolites. Liver tissue is adducted in vivo by 14CCl3NO2 (43% radiocarbon unextractable with methanol at 1 h), but the total radiocarbon content decreases 4-fold between 1 and 48 h after treatment. Liver effects from a high CCl3NO2 dose are associated with 19% less GSH and 50% more absorbance from soluble hemoproteins than controls. The toxicity of CCl3NO2 is probably due to disruption of multiple targets by its cascade of dechlorination products.

Evaluating Soil Solarization for Weed Control and Strawberry (Fragariaxananassa) Yield in Annual Plasticulture Production

“…Chloropicrin has a low odor threshold and causes sensory irritation at very low concentrations, so it has been added as a warning agent to other fumigants like methyl bromide and sulfuryl fluoride which are odorless. Chloropicrin's mechanism of action is not well understood, but it may be related to its reaction with biological thiols like glutathione and hemoglobin (Sparks et al, 1997). Chloropicrin also inhibits pyruvate and succinate dehydrogenase (Sparks et al, 2000).…”

“…At 1 hour and 48 hours, the liver had the highest level of radioactivity, followed by the kidney, lung, blood, fat and skin. Sparks et al (1997) also investigated the reaction of chloropicrin with biological thiols in vitro. Chloropicrin reacted quickly with various biological thiols including glutathione (GSH), cysteine, N-acetylcysteine, coenzyme A and reduced lipoic acid.…”

“…The proposed pathways for reaction of chloropicrin with GSH and Hb are shown in Figure 1. (Sparks et al, 1997) In a subsequent study, Sparks et al (2000) administered chloropicrin intraperitoneally to male Swiss-Webster mice at 5 mg/kg with DMSO as the vehicle and kept them in metabolic chambers for 24 hours. They were able to identify raphanusamic acid (also known as 2 thioxothiazolidine-4-carboxylic acid, TTCA) in the urine that was equivalent to about 1% of the administered dose of chloropicrin.…”

“…In a standard dermal irritation test in rabbits, they determined that chloropicrin was corrosive based on necrosis at 72 hours. Sparks et al (1997) determined the LD 50 for chloropicrin in mice to be 8 mg/kg after intraperitoneal injection. They also estimated the LD 50 for the metabolites, CHCl 2 NO 2 , CH 2 ClNO2 and CH 3 NO 2 .…”

Community Exposure Following a Drip-Application of Chloropicrin

“…7,8 Used in concentrations greater than 2%, chloropicrin is considered an active biocidal ingredient rather than a warning agent. 6 It can be mixed with other halogenated fumigants, including methyl bromide (18 products, 20% to 55% chloropicrin), dichloropropene (15 products, 15% to 60% chloropicrin), and methyl iodide (6 products, 0% to 75% chloropicrin).…”