Toxicologic evidence of developmental neurotoxicity of environmental chemicals

Abstract

Developmental neurotoxicity constitutes effects occurring in the offspring primarily as a result of exposure of the mother during pregnancy and lactation. To exert their effect, these chemicals or their metabolites must pass the placenta and/or the blood-brain barrier. In experimental animals, exposure to neurotoxic chemicals during critical periods of brain development has induced permanent functional disturbances in the CNS. Although available data suggest that proper animal models exist, only few chemicals have been tested.Neurotoxicity testing is not required by national authorities for classification of chemicals.Epidemiological evidence is very limited, but severe irreversible effects have been observed in humans following in utero exposures to a few known developmental neurotoxicants. The large number of chemicals with a potential for developmental neurotoxicity in humans stresses the importance of generating basic kinetic data on these chemicals based on relevant experimental models. First of all, data are needed on their ability to pass the placenta and the developing blood-brain barrier, to accumulate, and to be metabolized in the placenta and/or the fetus. These kinetic data will be essential in establishing a scientifically based hazard evaluation and risk assessment.

Pesticide Exposure and Stunting as Independent Predictors of Neurobehavioral Deficits in Ecuadorian School Children

“…[11][12][13][14]40,53 However, despite the extensive literature on pesticide poisonings in adults, very limited information is available on the effects of pesticides on the developing brain in humans. 1,2 Part of the reason for this lack of information is undoubtedly that the most widespread pesticide exposures occur in developing countries, where epidemiological studies may be difficult to carry out and where malnutrition and other potential confounders may compromise the results. On the other hand, extensive evidence has been gathered on the neurobehavioral consequences of malnutrition and stunting, [4][5][6]19,54 but these studies have not included pesticide exposure as a relevant cofactor that could impact on child development.…”

“…1,2 In an anthropological study of children living in a Mexican community with pesticide exposure and one without, the draw-a-person test was administered; the random undifferentiated lines drawn by the exposed children averaged only 1.6 body parts per figure, whereas nonexposed children produced reasonably lifelike figures, averaging 4.4 body parts each. 15 However, the exposure classification was based only on residential proximity to farms that used high quantities of organophosphate, organochlorine, and pyrethroid insecticides.…”

Non-precautionary aspects of toxicology

“…Furthermore, not all potential adverse effects are included in the tests required by the authorities. For example, neurotoxicity tests (in chicken) are normally required only for cholinesterase inhibiting pesticides [6]. Thus, even for those chemicals that have been tested, limited information exists on how those substances can influence human health at environmental levels of exposure.…”

Birth Weight in Relation to Maternal Blood Levels of Selected Elements in Slovenian Populations: A Cross-sectional Study

“…Among the most susceptible groups are pregnant women and children, the latter because of their increased exposure to mixtures of chemicals, increased absorption rates and a diminished ability to detoxify many exogenous compounds, all relative to those of adults [6]. The developing foetus is particularly susceptible due to partial lack of the blood-brain barrier [7] and to the rapid and tightly controlled growth of the brain during the pregnancy period [6]. The potential risk to the developing foetus is reflected in the level of contaminants in the maternal blood.…”