Effect of dosing vehicle on the dermal absorption of fluazifop-butyl and fomesafen in rats in vivo

Physicochemical and Biological Data for the Development of Predictive Organophosphorus Pesticide QSARs and PBPK/PD Models for Human Risk Assessment

A search of the scientific literature was carried out for physiochemical and biological data [i.e., IC50, LD50, Kp (cm/h) for percutaneous absorption, skin/water and tissue/blood partition coefficients, inhibition ki values, and metabolic parameters such as Vmax and Km] on 31 organophosphorus pesticides (OPs) to support the development of predictive quantitative structure-activity relationship (QSAR) and physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models for human risk assessment. Except for work on parathion, chlorpyrifos, and isofenphos, very few modeling data were found on the 31 OPs of interest. The available percutaneous absorption, partition coefficients and metabolic parameters were insufficient in number to develop predictive QSAR models. Metabolic kinetic parameters (Vmax, Km) varied according to enzyme source and the manner in which the enzymes were characterized. The metabolic activity of microsomes should be based on the kinetic activity of purified or cDNA-expressed cytochrome P450s (CYPs) and the specific content of each active CYP in tissue microsomes. Similar requirements are needed to assess the activity of tissue A- and B-esterases metabolizing OPs. A limited amount of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CaE) inhibition and recovery data were found in the literature on the 31 OPs. A program is needed to require the development of physicochemical and biological data to support risk assessment methodologies involving QSAR and PBPK/PD models.

Estimation of atrazine in the stratum corneum and its toxic effects in skin following topical application to rabbits

ABSTRACT For risk assessment, a workable non-invasive method for the estimation of atrazine in skin was needed. Moreover, the dermato-toxic effects of different concentrations of atrazine have not been studied so far. Fifteen milligrams of 35% solution of atrazine in ethanol was topically applied to each of six different clipped sites on the back of rabbits (n = 6). Each site was tape-stripped with 10 consecutive adhesive tapes at 0.5, 1, 2, 3, 4, and 6 h of topical dosing to remove the stratum corneum (SC). Atrazine in tapes was extracted with methanol and analyzed with HPLC. The amount of atrazine detected in the SC at 6 h (1955.79 +/- 47.22 mug) is equivalent to 13.03% of the total applied dose. In dermal toxicity studies, 500 mul of 35%, 70% atrazine in ethanol and a commercial preparation of atrazine (Balance(R)) was dosed on clipped backs of rabbits (n = 4) for 4 days under occluded vs non-occluded conditions. Ethanol alone served as control. On the 5th day, rabbits were euthanized and skin was scored for erythema and then examined microscopically. Significant differences (p < 0.05) in erythema scores were observed with 70% atrazine and Balance(R) as compared to the control under occluded conditions. Significant differences in epidermal thickness and cell layers were observed with Balance(R) and 74% atrazine as compared to control in both dosing conditions. There were non-significant differences in erythema, epidermal thickness, or cell layers in occluded vs non-occluded applications of atrazine in ethanol, indicating that atrazine is equally toxic regardless of its application procedures. Moreover, under non-occluded application, very slight erythema was observed but microscopically significant epidermal hyperplasia was noticed. This indicates that even if there are no significant gross skin manifestations of atrazine this can still produce significant damage to the epidermal barrier and hence can result in increase in penetration of self or other toxic substances.