Exposure potential Steps of pre-market risk assessment of pesticides

Public Health Significance of Urban Pests 509 percentages, can be used to express risk as a function of hazard and exposure. Risk assess- ments usually apply tiered modelling approaches that range from deterministic model- ling based primarily on conservative assumptions Tier 1 to probabilistic models that use refined assumptions based on real data Tier 3. Pesticide risk assessments apply conser- vative assumptions that overestimate exposure and hazard, resulting in a quantitative assessment that has a large margin of safety. The conservatism of these approaches is sup- ported by surrogate data; for example, exposure often can be estimated by using surro- gate data developed previously for other chemicals or an exposure database can be used for a surrogate estimate of inhalation and dermal exposure for many exposure scenarios. Relatively few studies in residential environments have examined the exposure of occu- pants to pesticides EPA, 1980. Most risk assessments are based on surrogate data and conservative assumptions EPA, 1998b, 1999, 2002a. To our knowledge, no study has compared the risk of disease from exposure to urban pests with the risk of pesticide expo- sure. These risk–risk and risk–benefit analyses would benefit greatly from more expo- sure studies on both of these topics.

14.7.1. Steps of pre-market risk assessment of pesticides

The first step in the risk assessment process identifies the uses of a pesticide from its pro- posed label such as use on lawns, use on carpets and crack-and-crevice treatment and how it is applied such as powder, spray or fogger. In the second step, the pesticide’s toxi- city is studied. The regulatory agency determines the most sensitive effect – the so-cal- led critical effect – for each exposure route and for several exposure durations such as acute and chronic. Next, all appropriate exposure scenarios are determined. Examples of scenarios include: • person spraying a liquid pesticide • person living in a house treated for insects. A registrant may be required to conduct exposure studies that address specific exposure scenarios for a specific chemical. If an exposure study that addresses a specific exposure scenario has not been conducted and a bridge to the existing use pattern is found unac- ceptable, scientists will use a model to evaluate available data, published literature, or some other source of information to develop a risk assessment for that scenario. A different modelling approach focuses on those exposed to pesticides who have not directly used them – that is, secondary exposures of bystanders. The premise of this model is that exposure levels are related to one’s activity while in a previously treated area and to the amount of pesticide available to the individual in that environment.

14.7.1.1. Exposure potential

Potential exposures may be measured or modelled, and each approach has advantages and disadvantages. Exposure measurements represent precise observations for a limi- ted number of cases: they can be carried out in the workplace, in the residential envi- ronment or through laboratory or workshop studies. Modelled exposures can be esti- Pesticides: risks and hazards 508 been assessed separately. As an exposure route, ingestion is currently weakly defined, though it may be the most important route in some circumstances. This is particularly true where inhalation and dermal uptake are low, where contaminated hands are not properly washed at the end of an application poor hygienic practice or where children have secondary exposure. A special case occurs when foodstuffs or food containers or plates and glasses are inadver- tently contaminated by spraying or direct contamination. Children spend a substantial part of their time walking and toddling indoors. Ingestion may occur by hand–mouth contact or by object–mouth contact. Such contact may be most prominent in young children, who show extensive mouthing behaviour around 1 year of age, when teeth erupt. Also, such contact transfers, to the mouth, pesticide residues, that have accumulated on hands or on objects. These may have come in contact with pesticide residues on such indoor surfaces as carpets, countertops or hard flooring or on lawns or other outdoor surfaces, such as soil. Oral non-dietary ingestion may be particularly important for infants and children exposed to lawn chemicals and household pesticide products in residential settings, because of the incidence of hand-to-mouth activity Hawley, 1985 or object-to-mouth activity Reed et al., 1999 and because of the activi- ties performed by children such as crawling that put them in close proximity to treated surfaces Cohen Hubal et al., 2000. Some assumptions and observations have been made for hand-to-mouth activity in children Reed, 1998; Zartarian, Ferguson Leckie, 1997, 1998; Zartarian et al., 2000; Tulve et al., 2002. Exposure from non-dietary ingestion may be estimated using residue data for the media of interest such as turf, soil or indoor surfaces and standard ingestion rates, based on the age group or activity of interest. Non-dietary ingestion can be assessed by using data on transferable residues for the surface area of the hands of children and also using stan- dard assumptions about the frequency of hand-to-mouth and object-to-mouth activity. The mass of residue ingested may be calculated for various age groups as the product of the transferable residue concentration in mgcm 2 , frequency of hand-to-mouth or object-to-mouth activity in eventsday, and contacted surface area from which residues are ingested in cm 2 event to yield the potential dose in mgday from hand-to-mouth transfer. Depending on the scenario of interest – that is, indoor or outdoor – dislodge- able residues should be assessed PMRA, 1998. Quantifying the intake rate from hand-to-mouth exposure is very difficult. Intake values have only been established for soil uptake, based on data collected in soil contamination study assessments that used chemical markers, although data specific to biocides have not been reported EC, 2002.

14.7. Pesticide exposure and risk assessment