Comparing pesticide risks from residential and dietary exposures

Public Health Significance of Urban Pests 517 large biomonitoring surveys of general populations, such as the survey conducted by the National Center for Environmental Health CDC, 2005 in the United States, that revea- led a widespread presence of small amounts of measurable pesticide residues in the urine of subjects who were not employed in agriculture nor were known to be professional users of pesticides. It is difficult to say how much the home use of pesticides and biocidal products contri- butes to the pesticide residues detected in general population surveys. In principle, the possibility that home use may be responsible for the urinary occurrence of pesticide resi- dues in some subjects and in others may add considerably to dietary exposure, cannot be excluded. However, the frequency and continuity basically daily of dietary exposure, when compared with the infrequent and discontinuous and relatively low level of resi- dential exposure for home use of biocides, make dietary exposure more likely blame- worthy than home exposure for the widespread pesticide residue contamination at the general population level.

14.8. Examples of residential risk assessments

This section covers understanding and comparing risks from routes of residential expo- sure, chlorpyrifos and pyrethrin exposures and risks, and a summary of examples of resi- dential risk assessments.

14.8.1. Understanding and comparing risks from routes of residential exposure

Housing residents are likely to be exposed to pesticides used in the home. The most com- mon routes of exposure are the dermal and inhalation routes, with unintentional inciden- tal oral exposure being attributable primarily to toddlers putting their fingers in their mouth after crawling over treated surfaces or touching pets. To better understand the Pesticides: risks and hazards 516 crack-and-crevice treatments; h pet treatments; i detergents; j impregnated mate- rials; k termiticides; l inhalation of residues from indoor treatments; and m rodenti- cides. Default values for the underlying exposure factors, such as amount used or der- mal transfer factors, are specified. These default values represent reasonable worst-case values. While the SOPs provide methods and default assumptions for conducting scree- ning-level residential exposure assessments for indoor and outdoor settings, they do not preclude the use of more sophisticated methods including stochastic analyses and the replacement of default values for exposure parameters with new data. WHOPES has published an easy to understand quantitative exposure and risk assessment for insecti- cide-treated mosquito nets, which provides a stepwise approach to assessing toxicity, exposure and risk WHOPES, 2004.

14.7.3.1. Comparing pesticide risks from residential and dietary exposures

When discussing exposure of the general population to pesticides, as a result of home use and application, it has to be kept in mind that dietary exposure to pesticide residues is known to occur in most parts of the world. This dietary exposure is regulated by law in most countries and is legally permitted in so far as it is considered to be safe or acceptable when the use of pesticides on specific agricultural products is authorized. Since such expo- sure involves millions of people, the regulating authorities in the various countries of the world have set up complex monitoring systems aimed at checking regularly the residues present on a large variety of food items sampled from the market. The results of this monitoring are collected and analysed periodically to ensure that the foods on the mar- ket comply with the legally established levels of residues and that the health risk for consumers remains within the limits set up by legislation. A general overview of the results produced by the residue monitoring systems indicates that the proportion of samples of food items found to be irregular is generally rather low and decreasing over time; for example, in the EU, from a frequency of detection of irre- gular samples of 5–6 typically observed in the mid-1990s, the actual frequency of detec- tion has decreased to 2–3 and in some countries to 1. Two major reasons account for a sample being defined as irregular. • A sample contains a pesticide residue permitted, but in a concentration slightly excee- ding the maximum residue limit MRL. • A food item contains the residue of a pesticide the use of which is not legally permitted for that crop. A toxicological assessment of such irregularities in pesticide residues suggests that the overall risk for the population is minimum, if any, given the margin of safety adopted in setting MRLs and the modestly excessive levels found in the samples. These population-level data, though reassuring in terms of toxicological risk, do indicate that consumers normally ingest pesticide residues with their diet, that only about 50 of the food items on the market do not have measurable residues in or on them and that a fair percentage of food items 10–20 bear more than one residue up to six at the same time. These analytical observations are in agreement with the results obtained by Table 14.2. Regulatory end-points and toxic effects of chlorpyrifos and pyrethrins Acute Sub-chronic Pesticide Regulatory end-point Toxic effect Regulatory end-point Toxic effect NOAEL NOAEL Chlorpyrifos Incidental oral route = Plasma and RBC a — Cholinesterase 0.5 mgkg cholinesterase inhibition inhibition Dermal route = Dermal route = 0.15 mgkgday 0.3 mgkgday Inhalation route b = Inhalation route b = 0.1 mgkgday 0.1 mgkgday Pyrethrins Inhalation route = Neurotoxicity Inhalation route Neurotoxicity 7.67 mgkgday LOAEL = 2.57 mgkgday Incidental oral route = Incidental oral route = 20 mgkgday 6.4 mgkgday a RBC = red blood cell. b As a conservative assumption, 100 lung absorption was assumed. Source: EPA 2000d, 2006a. Public Health Significance of Urban Pests 519

14.8.2. Risk assessment of residential exposures to chlorpyrifos