Review of main points

Public Health Significance of Urban Pests 527

14.10. Review of main points

Risk assessment is a formal means of evaluating risk in an objective manner by conside- ring uncertainties and assumptions. Risk, as a function of hazard and exposure, can be expressed in quantitative terms. Risk assessments usually apply tiered modelling approa- ches that range from deterministic modelling based primarily on conservative assump- tions Tier 1 to probabilistic modelling that uses refined assumptions based on real data Tier 3. Pesticide risk assessments apply conservative assumptions that overestimate exposure and hazard, resulting in a quantitative assessment that has a large MOS. The conservatism of these approaches is supported by surrogate data, because there have been relatively few studies in residential environments that have examined the exposure of occupants to pesticides. The objective of this chapter is to examine human health risks from indoor pesticide exposure in residential settings. Due to the intrinsic toxicity of pesticides, the need for strict regulation of their admission to the market and their use has been recognized for a long time. Also, in most countries specific and complex legislation prescribes a thorough risk assessment process prior to their entrance in the market, to guarantee health safety for consumers and protection of the environment. Pesticides are regulated nationally and internationally as toxicants. In Europe and North America, the ECB, EPA, and PMRA are the principle pesticide regulatory agencies. A legal regulatory framework also exists in most individual states. This framework inclu- des standardized approaches to risk characterization, and many decisions are made in a forum that includes the general public and other stakeholders. This framework and asso- ciated regulatory processes ensure a thorough review of pesticidal effects, and exposure and use patterns, to fully characterize risks to workers and the general public. Special consideration is given to children, pregnant women and other sensitive sub-populations. In many regulatory agencies, the precautionary principle is applied where uncertainty exists, and alternatives to more toxic pesticides are given priority in regulatory reviews and registration. Post-marketing risk assessment takes place after a pesticide has been put on the market and is aimed at evaluating the safety of the actual conditions and pattern of use. That some pesticides are being removed from the market due to unacceptable intrinsic toxi- city does not have to be regarded with concern. On the contrary, it represents a part of a complex approach to consumer protection and has to be addressed as part of the larger pesticide regulatory framework to prevent risks to human health. The first two steps in the risk assessment process are identifying the hazard and descri- bing the dose–response relationship. These steps establish the toxicological profile of the pesticide, based primarily on standardized toxicity testing in animal models. Acute, sub- chronic and chronic testing describes the short-term and long-term effects from expo- sure by the oral, dermal and inhalation routes. However, to date, standardized testing in animal models has not been effective in predicting human responses to pesticide exposure that cause allergenic or neuropathic effects. Furthermore, the development of animal and computer models to detect and understand possible, if any, relationships between pesti- Pesticides: risks and hazards 526 toxicity studies. Pesticide exposure is always much higher in these studies than any expec- ted exposure in people. Where possible, studies are conducted that determine or can pro- vide a hint about the cancer-causing mechanism. The outcome of these animal studies is used in a so-called weight-of-the-evidence approach, to decide if a pesticide is likely to have carcinogenic effects in people. Risk management is applied to further mitigate any risks. The quantitative assessment of the risk of cancer requires the use of sophisticated statis- tical models to estimate its potential at the lower levels of exposure seen in people. A model used widely for regulatory purposes is the linearized multistage model. This model results in an expression of a unit risk of cancer, Q1 known as a Q-star, that allows the calculation of the likelihood or probability of cancer lifetime cancer risk for an average daily lifetime exposure. For example, a 1x10 -6 risk of cancer means that an individual has a one in a million chance of developing cancer from an average daily lifetime exposure to a particular pesticide. The acceptability of the risk of cancer is a risk management decision that cannot rely exclusively on a numerical standard, but needs to take into consideration all the factors that influence the risk. From the historical actions of regulatory agencies, it is recognized that areas of regulatory concern for the lifetime risk of cancer are in the neighbourhood of 10 -4 to 10 -6 one in ten thousand to one in a million. A lifetime risk of cancer that is below one in a million usually does not indicate an unacceptable risk for the general popu- lation – and to otherwise unintentionally exposed people, such as housing residents – when exposure occurs through pesticide residues in or on food. In some instances, can- cer risks in the range of 1x10 -5 to 1x10 -6 one in one-hundred thousand to one in a million have been tolerated for industrial workers exposed occupationally to carcinogenic che- micals. These risk ranges are used by pesticide regulators as benchmarks to guide them through decisions about the acceptability of the lifetime risk of cancer. Both types of pesticide risk benchmarks, the MOS approach and the quantitative cancer risk assessment, provide estimates of risk that arise from defined exposures. Usually the estimate reflects a so-called typical exposure and use situation, taking into consideration whether the exposure is occasional or frequent and of short or long lifetime duration. The estimate is kept conservative by generally overestimating exposure and risk and by using many so-called worst case assumptions, such as assuming that 100 of the airborne pesticide exposure would be inhaled and absorbed or that all applicators will make appli- cations at the maximum application rate, or that 100 of the pesticide deposited on the skin would penetrate through the skin. These benchmarks serve as a basis for regulatory decision-making and aid in residential risk-management approaches. Public Health Significance of Urban Pests 529 When discussing exposure of the general population to pesticides, as a result of home use and application, it has to be borne 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 accepta- ble when the use of pesticides on specific agricultural products is authorized. Since such exposure concerns millions of people, regulating authorities throughout the world have set up complex monitoring systems aimed at regularly checking 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 market 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 findings of residue monitoring systems indicates that the pro- portion of samples food items found to be irregular is generally rather low and is decrea- sing over time: for example, in the EU, from a frequency of detection of irregular sam- ples of 5–6 typically observed in the mid-1990s, the actual frequency of detection has decreased to 2–3, and in some countries to 1. Among the reasons for a sample to be defined irregular, two major circumstances may occur that result in this classification: a a sample may contain a permitted pesticide residue, but in a concentration slightly excee- ding the respective MRL; or b a food item may contain the residue of a pesticide the use of which is not legally permitted for that crop. A toxicological assessment of such irre- gularities in pesticide residues suggests that the overall risk for the population is mini- mum, if any, given the MOS adopted in setting the MRLs and given the modestly excee- ded levels found in the samples. These data at the population level, 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 obtai- ned by large biomonitoring surveys of the general population, which have revealed a widespread presence of small amounts of measurable pesticide residue 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, both the relative frequency and continuity of dietary exposure basi- cally daily, when compared with the infrequent and discontinuous home use of biocides, and the relatively low level of residential exposure, when compared with dietary expo- sure, make dietary exposure more likely blameworthy than home exposure for the widespread pesticide residue contamination at the general population level. Cancer from exposure to pesticides has long been a concern of regulators and public Pesticides: risks and hazards 528 cide exposures and endocrine disruption is still in its infancy. Another area of uncertainty concerns the interaction of pesticides with inert ingredients in formulations. Currently, these effects are quantified for acute exposures, but toxicity evaluations by regulatory agencies continue on inert ingredients. Quantifying exposure to pesticides is essential to characterizing and managing risk. Because risk generally increases with exposure, exposures from the oral, inhalation, and dermal routes must be determined. To evaluate risk, a risk assessment integrates hazard and exposure. An MOS is calculated as a function of hazard and exposure and AELs are applied as precautionary measures to ensure an adequate MOS, to minimize risks from pesticide exposures. For most assessments of the residential risk of pesticides, the AEL equals 1000. This exposure is 1000 less than the NOAEL derived from animal testing. For residents exposed to pesticides used in the home, the dermal and inhalation routes are the most common routes of exposure, with unintentional incidental oral exposure attri- butable primarily to toddlers putting their fingers in their mouth after crawling over treated surfaces or touching pets. To better understand the magnitude of exposures by the principal routes, together with their significance in light of application use patterns, we provided examples from EPA exposure evaluations and cited public literature. Risks from residential pesticide use and exposure are affected by a number of factors, including: the hazard and the residual quality of the pesticide applied; the amount of AI applied per unit area; the application method; the formulation type; and the route or rou- tes of exposure. Exposures to chlorpyrifos and pyrethrins and the corresponding risks were described to illustrate the evaluation process. For chlorpyrifos, exposure took place at the time of application and for weeks thereafter, even with crack-and-crevice treat- ments. On the other hand, due to the low application rates and to pyrethrins being short lived, exposure was minimal by the inhalation route, and dermal exposure was not a concern. Based on these assessments and the weight of the scientific evidence, the risk of pesticide use and pesticide application by consumers in residential environments usually does not exceed a level of concern. Compared with agricultural applications, residential applica- tions of pesticides are made at much lower rates and use application methods designed to minimize direct or incidental exposures. However, assessments of residential pestici- des, such as chlorpyrifos, show that some pesticides are unsafe. The chemical nature of a pesticide and its patterns of use can result in significant expo- sure concerns. Such concerns have fuelled the regulatory review of all pesticide chemi- cals and led to extensive international efforts to protect sensitive sub-populations, such as children, pregnant women and people sensitive to chemicals. This concern has also led to the application of the precautionary principle to the regulatory decision-making pro- cess. Where uncertainty exists, caution is used as a regulatory measure to ensure that exposures to pesticides do not cause adverse effects. IPCS is coordinating efforts to har- monize international approaches to hazard, exposure and risk assessment. Public Health Significance of Urban Pests 531 • Store clothes with moth repellents in separately ventilated areas, if possible. • Keep indoor spaces clean, dry and well ventilated to avoid pest and odour problems. Unless you have had special training and are certified, never use a pesticide that is res- tricted to use by state-certified pest control operators. In conclusion, indoor applications of pesticides, which are regulated by a complex risk assessment before and after they are put on the market, do not pose a high level of risk to human health if the application of the product and the management of the application take place according to proper and adequate procedures. This adherence to proper pro- cedures, together with recent efforts to produce pesticides with a lower overall toxicity, is able to reasonably assure the absence of any unacceptable risk to human health and the environment. To our knowledge, no studies have considered which risk is worse: the risk of disease from exposure to urban pests or the risk of pesticide exposure. These risk–risk and risk–benefit analyses would benefit greatly from more exposure studies on both of these topics.

14.11. Future actions and data development