ARTICLE IN PRESS Int. J. Hyg. Environ.-Health 210 (2007) 169–176 www.elsevier.de/ijheh Effects of separate and combined exposure to the pesticides methamidophos and chlorothalonil on the development of suckling rats Vera Lu´cia Scherholz de Castroa,Ã, Selma Heloı´sa Chioratob aEmbrapa Environment, Rodovia SP 340, km 127,5, Jaguariu´na, SP, 13820-000, Brazil bSchool of Veterinary Medicine and Zootechnics, University of Sa˜o Paulo, Sa˜o Paulo, Brazil Received 9 February 2006; received in revised form 15 September 2006; accepted 21 September 2006 Abstract It has been suggested that, in some cases, exposure to environmental contaminants affects children more profoundly than adults. It is important to evaluate adverse health outcomes in children, a population susceptible to toxic chemicals and mixtures. We examined the effects that maternal exposure to two pesticides had on maturational aspects of offspring development during the nursing period. Nursing female rats were exposed to 1–4 mg/kg of intraperitoneal methamidophos, 200–800 mg/kg of chlorothalonil, or both. The higher doses of methamidophos affected pup viability by day 21 of life. Both pesticides, alone or together, affected body weight gain of dams and offspring. Developmental milestones evaluated in the pups were incisor eruption, ear unfolding, eye opening and testis descent. Although no clear dose–response relationship was established between these milestones and exposure to methamidophos or chlorothalonil, incisor eruption was accelerated in many groups, and the majority of rat offspring exposed to methamidophos presented later ear unfolding and eye opening than did the control group offspring. Sexual maturation (testis descent) was significantly delayed in some groups. For dams and pups alike, simultaneous exposure to both pesticides was not found to have a greater toxic effect than that resulting from exposure to only one of the two. Taken together, these results demonstrate exposure-related influences on several developmental measures. Detection of more subtle effects may be improved through the use of the developmental temporal response protocols utilized in this study. r 2006 Elsevier GmbH. All rights reserved. Keywords: Methamidophos; Chlorothalonil; Suckling rats; Pesticide mixtures; Physical milestones; Perinatal exposure Introduction present simultaneously in breast milk. The quantity of pesticide that is passed to the infant via breast milk is Poisoning in newborns has been associated with influenced by many variables (Weiss et al., 2004). maternal exposure to pesticides at the place of residence Age-dependent variations in susceptibility appear to or in the workplace (Whyatt et al., 2002; Cerrillo et al., depend on the chemical of concern, the effect that is 2005; Ribas-Fito´et al., 2005). Multiple pesticides can be evaluated, the level/duration of exposure and the developmental period during which the exposure occurred (Scheuplein et al., 2002). It is also noteworthy ÃCorresponding author. Tel.: +55 19 3867 8739; fax: +55 19 3867 8740. that infants may be more susceptible to neurobehavioral E-mail address: [email protected] (Vera Lu´cia Scherholz alterations, which may not be apparent until later in life de Castro). (Moser et al., 2001; Scheuplein et al., 2002; Costa et al., 1438-4639/$ - see front matter r 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2006.09.003 ARTICLE IN PRESS 170 Vera Lu´cia Scherholz de Castro, S. Heloı´sa Chiorato / Int. J. Hyg. Environ.-Health 210 (2007) 169–176 2004). For example, in experimental models, developing toxicological observations suggest that OP insecticides animals have been shown to be more susceptible have biological effects other than their cholinesterase- than adult animals to the acute toxicity of the inhibitory properties. The use of other end measures organophosphate (OP) pesticide chlorpyrifos, which could increase the ability to identify toxic responses to can cause neurobehavioral abnormalities (Richardson chemicals polluting the workplace and the general and Chambers, 2005). environment. When two or more chemicals are applied simulta- In contrast to the relatively extensive knowledge neously to a living system or unit, the combined effect regarding OP compounds, there are no well-defined can modify the individual toxic effect, since they might biomarkers of the effects of chlorothalonil. Despite the have cellular targets or metabolic pathways in common. fact that mixtures (including chlorothalonil) simulating Despite the fact that almost all chemical exposure of groundwater contamination have been shown to reduce humans is to mixtures, and that such mixed exposure blastocyst development and the mean number of occurs in the context of numerous other risk modifiers, blastocysts per embryo (Greenlee et al., 2004), chlor- the current understanding of human health risks is othalonil toxicity has been evaluated only in adults. based almost entirely on the evaluation of chemicals Since chlorothalonil has the potential to promote studied in isolation. Under realistic environmental hepatic and renal damage (Suzuki et al., 2004) and conditions, concomitant or sequential exposure to consequently alter drug metabolism and excretion, it pesticide mixtures dictates the need for exposure might be expected that the toxicity of methamidophos assessment, hazard identification and risk assessment would be altered when there is concurrent exposure to (Cory-Slechta, 2005). the two pesticides, especially during lactation. Attempts to deal with the problem of chemical Owing to the present lack of information concerning mixtures have largely been restricted to classes of the effects of mixtures of toxicants on postnatal chemicals that are structurally related. While an development, we studied the effects that exposing dams intraclass focus may be a logical starting point for to chlorothalonil and methamidophos mixtures had on evaluating the toxicity of chemical mixtures, it encom- suckling rats. To that end, we constructed dose–re- passes only a small fraction of the aggregate or overall sponse curves for one compound in the presence of a exposure problem. The breadth of classes and types of range of doses of the other. chemicals to which humans are exposed are not Since it has been established that the first three weeks structurally-related chemicals (Cory-Slechta, 2005). Bet- postpartum include a period of brain growth, during ter understanding of the patterns of exposure and the which the most rapid development of cholinergic underlying variability within the human population, as neurons occurs in the rat brain (Tang et al., 2003), we well as the links between the animal toxicology data and studied the effects that lactational exposure to various human health effects, will improve the evaluation of mixtures of methamidophos and chlorothalonil had on risks to human health posed by pesticides mixtures suckling rats between postnatal days (PND) 1 and 21. (Lima, 2003; Mumtaz et al., 2004). The dams were exposed intraperitoneally during lacta- The OP insecticide methamidophos and the fungicide tion, which results in first-pass metabolism in the liver. chlorothalonil are commonly used in agriculture and are There is some evidence that methamidophos, acting frequently sprayed simultaneously on various crops, directly or as a metabolite, is a potent liver carbox- including tomatoes (Castro et al., 1999). The neurotoxic yamidase inhibitor in mammals (Mahajna et al., 1997). potential of OP insecticides has been described by Chlorothalonil has been shown to induce lipid perox- various authors (Farahat et al., 2003; Smulders et al., idation in rat hepatocytes in vitro and has been 2004). These insecticides exert acute toxicity primarily classified as a human carcinogen of intermediate through persistent inhibition of acetylcholinesterase potency (Lodovici et al., 1997). (AChE) at cholinergic junctions within the central and peripheral nervous systems. Although AChE is the clinically significant target of OP exposure, other proteins also form covalent bonds with OP insecticides, Materials and methods depending on the chemical properties of the insecticide (Peeples et al., 2005). However, the toxicological Animals relevance of the inhibition of these secondary targets is not yet understood. In addition, there are examples of Ninety-day-old Wistar male and nulliparous female signs of toxicity unaccompanied by AChE inhibition. In rats from our own colony, weighing 250730 g, were experimental animal models, doses that are too low to used. Females were housed individually in polycarbo- produce cholinergic signs have been shown to produce a nate cages with hardwood chip bedding and were given variety of effects, ranging from enhanced maze learning free access to tap water and food. Within the facilities, to slowed nerve conduction (Peeples et al., 2005). These the environment was controlled (room temperature: ARTICLE IN PRESS Vera Lu´cia Scherholz de Castro, S. Heloı´sa Chiorato / Int. J. Hyg. Environ.-Health 210 (2007) 169–176 171 2272 1C; humidity: 70%), and a 12 h light/dark cycle highest dose caused some weight reduction in the dams was maintained. The animals were fed a commercially and resulted in pup death at the end of the exposure prepared laboratory diet (Purina Lab Chow). The period. P-generation breeders of our own colony come from Since there were no signs of toxicity promoted by Cemib–Unicamp facilities (Campinas, Brazil), which is chlorothalonil exposure, only the highest one was tested recognized by the International