Assessing exposure of young Australian children to toxicants in the home environment using a web-based questionnaire

Abstract

The presence of endocrine disrupting chemicals (EDCs) in the home environment is ubiquitous and is a major contributor to the exposure of young children to these chemicals. EDCs are found throughout the domestic environment, including in consumer goods, dust, air and food. Whilst the term EDCs refers to chemicals that have been demonstrated to disrupt the normal homeostasis of the endocrine system, they also affect a variety of other systems.Epidemiological evidence suggests that exposure to EDCs during the foetal period and childhood may be contributing to the increasing incidence of non-communicable diseases, such as obesity, during childhood and possibly later in life. However, to date, little research has been conducted in Australia to assess exposure of young (less than three years old) children to EDCs and associated health outcomes. The current ‘gold standard’ of assessing human exposure to these chemicals is biomonitoring. Biomonitoring in environmental epidemiology studies of children is ethically and practically challenging. There is a pressing need to develop alternative practical and accurate exposure assessment methods for use in large-scale children’s environmental epidemiology studies.The aim of this PhD was to explore the feasibility of online questionnaires as an alternative method of exposure assessment – by designing a household-level exposure-assessment questionnaire and then administering it in conjunction with human biomonitoring. The feasibility testing was conducted for two selected groups of EDCs, insecticides, with the pyrethroids and organophosphates as the chemicals of interest, and polybrominated diphenyl ether flame retardants (PBDEs). Plastics, with bisphenol A and phthalates as the focus, were included in the questionnaire design phase of this thesis, but were then excluded from the questionnaire in the human biomonitoring study to reduce its length.To identify potential determinants of exposure to be included in the exposure-assessment questionnaire extensive literature reviews were conducted. However, the information obtained from literature reviews alone was insufficient to ensure the content validity of the questionnaire, since data on EDC exposure pathways in Australian households were scarce and international data is not necessarily generalisable to the Australian context. Additional primary research was therefore undertaken in Queensland, Australia, to obtain more information on insecticide exposures. A more extensive literature review was also undertaken with a specific focus on the flame-retardant BDE-209.The questionnaire was then designed and pre-tested. After this phase, plastics were removed from the questionnaire to reduce its total length. To assess the feasibility of the approach, the questionnaire was administered in a questionnaire-biomonitoring study of 61 families with children aged <2 years (at the time of recruitment) from Brisbane and Toowoomba, QLD. Practical aspects of questionnaire administration were assessed and the content validity of the questionnaire was examined by assessing the association between questionnaire data and human biomonitoring data via linear regression modelling.The PBDE flame retardants as a group failed to meet many of the criteria important for effective exposure-assessment questionnaires during the design phase of the questionnaire. Despite the extensive literature reviews conducted in this PhD, many gaps in our knowledge of PBDE sources and exposure pathways exist for young children. Of the known possible sources, many of these cannot be confidently identified via a questionnaire. Since there are multiple sources and exposure pathways (including historical and maternal exposures) that contribute to PBDE body burdens in children, it is not feasible to measure all of these in a questionnaire. Finally, in the questionnaire-biomonitoring study, associations between questionnaire data and PBDE biomonitoring concentrations were not consistent with exposure determinants that had previously been identified. Biomonitoring therefore remains the exposure assessment method of choice for PBDEs.There was a relatively greater body of work examining young children’s exposure to insecticides and more Australian data about likely sources were identified via the literature reviews and the analysis of calls to the Queensland Poisons Information Centre. In contrast to PBDEs, the major pathways of exposure to insecticides, including diet and domestic pest-control product use, were readily assessable via the questionnaire. In the questionnaire-biomonitoring study, the associations between biomonitoring data of insecticide concentrations and questionnaire data were generally consistent with determinants that were identified in the questionnaire design phase. These findings suggest that questionnaires may be a feasible method of insecticide exposure assessment in young children. Based on this assessment, a formal validation study for the insecticide component of the questionnaire is indicated.In summary, the questionnaire-based approach to exposure assessment may be feasible when comprehensive exposure pathway data for the chemical of interest are available, when the total number and complexity of exposure pathways is limited, and when sources are readily identifiable via a questionnaire.