Inhalation Routes of exposure

Public Health Significance of Urban Pests 505 The airborne concentration of a biocidal product sprayed in an enclosed space, varies according to the ventilation of the room during and after the application, the concentra- tion decay over time being directly related to the rate the air in the room is changed Fenske et al., 1990. After application, the airborne chemical may diffuse onto surfaces such as walls, furniture and floors and into sorptive media such as textile materials, curtains, carpets and plush toys, from which it can be subsequently re-emitted for quite a long time. For example, Gurunathan and colleagues 1998 showed that after applica- tion indoors, chlorpyrifos residues increased on the surface of plastic toys and peaked at one week after application. The user’s exposure via inhalation primary exposure should be measured, using perso- nal monitoring, to assess the airborne concentration in the breathing zone by conven- tion within 30 cm of the nose and mouth. This measurement is incorporated into inha- lation exposure risk assessments. Exposure of others, as a consequence of use secondary exposure, is often evaluated either by using static background monitoring or mathematical models, which are used more frequently. Secondary exposure by inhalation is generally expressed by the time-weigh- ted average of a particular substance in mgm 3 , over a defined period of time. Few validated methods relate exclusively to monitoring air and the determination of bio- cidal agents. Less than 10 of the substances listed by the EC in its provisional list of exis- ting biocidal substances have been found to have specific workplace measurement methods as vapour or aerosol. The important criteria and appropriate selection of sampling devices are outlined in a review by Findlay 1995. Other relevant texts include the European Committee for Standardization CEN standard on workplace atmospheres CEN, 1995, the Deutsche Forschungsgemeinschaft DFG publication on analysing hazardous substances in air DFG, 1993 and the Health Safety Executive HSE publications on methods for deter- mining hazardous substances HSE, 2007.

14.6.2. Dermal exposure

Exposure of and via the skin is usually a significant aspect of human exposure to bioci- des. While this has been commonly considered for risk assessments of plant protection products, it is not so for biocides. Exposure data for deposition of biocides on work clo- thing and exposed skin have only recently been established. The pattern of distribution over the body differs with the task – for example, sometimes only the hands are exposed. The concepts of potential dermal exposure, estimated exposure and actual dermal exposure are used to gauge exposure. Potential dermal exposure . This is the amount of biocide that may deposit on the clothes and on exposed skin over some defined period of time. Common metrics include mg AI Pesticides: risks and hazards 504

14.5.4. Assessing residential exposure

Addressing exposure of the general population and particularly of children is a com- plex task. Because of the many ways in which non-dietary residential exposure can occur, the EPA has developed standard operating procedures SOPs for residential exposure assessment, to add consistency and transparency to the risk assessment and regulatory process and to provide guidance to scientists. The SOPs address over 40 different expo- sure scenarios, were developed using the most recent data available and provide a so-cal- led handbook approach, by presenting a description of each scenario along with recom- mended algorithms, sample calculations, a discussion of uncertainties and references. All exposure scenarios addressed in the EPA’s SOPs EPA, 1997a are non-occupational. Exposure of bystanders from occupational applications or from bring-home events to children such as spray drift and residue track-in are also being considered by the EPA Office of Pesticide Programs, as they may expose individuals not involved in the occu- pational activity such as children of farmers or pest control operators. The EPA’s residential exposure assessments are designed to be as realistic as possible. They are, however, generally conservative, which adds an extra measure of safety to regu- lating pesticides. More recently, the EC has developed guidance EC, 2002 that addres- ses a variety of exposure scenarios.

14.6. Routes of exposure

This section covers three routes of exposure: inhalation, dermal exposure, and inciden- tal oral exposure.

14.6.1. Inhalation

Exposure from inhaled pesticides is sometimes a small component of total exposure to biocides, but it can in some cases become the predominant route of exposure. Conditions where exposure through inhalation becomes important, usually involve the use of vola- tile biocides or of dusts, fumigants and sprays, especially in enclosed spaces. It should also be borne in mind that a higher proportion, up to 100, of the inhaled dose may be bio- available, compared with a lower percentage absorbed by dermal exposure. The assessment of inhalation exposure is well characterized by standard metrics and sam- pling methods. Because there is a large body of national guidance and scientific litera- ture on conducting surveys to determine exposure to vapours and aerosols by inhalation, this matter is not developed further in the present chapter. It is important, however, to have some knowledge of the likely distribution of particle sizes of an aerosol generated from a solid product. Also, because some biocides have a low, but nonetheless significant vapour pressure, and because deposits on air sampling filters can evaporate into the sam- pled air stream, special sampling techniques are required. Public Health Significance of Urban Pests 507 not account for the rate of accumulation on the skin. Dermal exposure data are difficult to acquire and interpret. However, methods are avai- lable for the sampling process, such as the WHO recommended methods developed for occupational exposure assessment WHO IPCS, 1999 and dermal absorption Kielhorn, Melching-Kollmuss Mangelsdorf, 2006. These methods make use, as in other methods, of a set of gauze pads applied to the skin of different parts of the body; the concentration measured in the pads is used to calculate the dermal exposure of each part of the body. Exposure of the hands is often highly significant. Although residential labels of several products recommend gloves as best management practice, homeowners can hardly be assumed to typically wear protective gloves when applying pesticides in the home. Moreover, poor procedures in putting on and taking off gloves can lead to significant exposure to the hands, regardless of the barrier properties of the protective glove mate- rial. Dermal exposure may also result from contacting treated areas. Even where a pesticide has been applied to cracks and crevices, its residues can be detected throughout the house, and contact may occur through everyday activities. For example, in a case where chlor- pyrifos applications had been made to the cracks and crevices of the homes and along the perimeters of the walls behind appliances and furniture, surface wipe samples collected from non-targeted surfaces such as play areas, bedrooms and plush toys showed the pre- sence of chlorpyrifos Hore et al., 2005. Sampling gloves provide a measure of potential dermal exposure when coming directly into contact with solids, fluids and aerosols; these gloves may over-sample, but they can reflect actual dermal exposure. Thin cotton sampling gloves worn beneath protective glo- ves demonstrate actual hand exposure but again may overestimate exposure. Sampling protocols, however, need to recognize that sampling gloves will collect pre-existing conta- mination inside protective gloves. Another technique for assessing hand exposure uses hand washing with solvent–water solutions and wiping the skin on the hand at the end of use see also Kielhorn, Melching-Kollmuss Mangelsdorf, 2006. Using surrogate biocide products, further research in progress will indicate the likely percentages and spatial distributions of typical work clothing penetration. Finally, it should be mentioned that washing contaminated clothing clothing used while applying biocides with everyday laundry might contaminate the household laundry or clothing.

14.6.3. Incidental oral exposure