Evaluation of the Developmental Toxicity of the Pesticide McPa and Its Contaminants Phenol and Chlorocresol

Abstract

The embryotoxicity of 4-chloro-2-methylphenoxyacetic acid (MCPA), an extensively used herbicide, has been evaluated and compared to that of phenol and chlorocresol (two common contaminants) with a bioassay that makes use of embryos of the amphibian Xenopus. The MCPA-Na salt used in the bioassay was purified by crystallization and acid-base purification methods, and the concentrations of phenol and chlorocresol were checked by high-performance liquid chromotography. The relationship between the concentration of the tested molecule and the outcomes (i.e., mortality and malformations) was investigated using different models (probit, logit, and complementary log-log). The resulting LC50s for MCPA, chlorocresol, and phenol are 3,607, 13, and 178 mg/L, respectively; the resulting LC10s are 1,526, 6, and 32 mg/L. It is evident that the real MCPA toxicity can be masked by the presence of contaminants much more toxic than the molecule studied. Moreover, our results show that the three chemicals do not present a high teratogenic risk. Growth retardation shows that MCPA, chlorocresol, and phenol are effective at concentrations as low as 2,000, 2.5, and 25 mg/L, respectively. Keywords-EmbryotoxicTeratogen Herbicide Xenopus EmbryoEnviron. Toxicol. Chem. 15, 1996 G. Bernardini et al.

Lethal and teratogenic effects of phenol on Bufo arenarum embryos

“…After 96 h of treatment, LC 50 , LC 99 and NOEC values (acute test) were 183.70, 250 and 60 mg/L, respectively. A concentration dependent increase in mortality was observed and these results are in agreement with those described by Bernardini et al, in Xenopus embryos [27], i.e. based on LC 50 values, B. arenarum showed a similar phenol tolerance as this species (LC 50 178 mg/L).…”

“…Indeed, a TI 50 value higher than 1.5, indicates teratogenic hazard [27]. Therefore, phenol is a teratogenic substance for B. arenarum embryos because its TI 50 is above this threshold (TI 50 = 1.62).…”

“…In addition, Birge et al and Black et al examined the toxicity of phenol on eight species of amphibians and found LC 50 values from 0.04 to 9.87 mg/L depending on the species studied [25,26]. Moreover, Bernardini et al described a LC 50 value of 178 mg/L for Xenopus embryos [27].…”

4-Chloro-2-Methylphenoxyacetic Acid Containing Compounds. Genotoxicity Evaluation by Mutatox® Assay and Comparison with Acute (Microtox®) and Embryo (FETAX) Toxicities

“…The MCPA Na salt was purified by crystallization and acid-base purification starting from 97% MCPA (Fluka Chemie AG, Buchs, Switzerland), and its purity concerning phenol and chlorocresol presence was checked by HPLC. Purified MCPA Na salt contained less than 0.04% (w/w) of phenol and less than 0.004% (w/w) of chlorocresol (Bernardini et al 1996).…”

“…Each was tested with and without S9 enzyme system activation. Moreover, we have compared the Mutatox data with those obtained using Microtox (acute toxicity test) and FETAX (Frog Embryo Teratogenesis Assay-Xenopus), previously performed in our laboratory Bernardini et al 1996). Correspondence to: C. Vismara…”