Introducing internal allocation factors for assessing aggregate pesticide exposure across multiple pathways and...

In the health risk assessment of pesticides, methods for external exposure assessment have been well developed. However, quantifying the contribution of various exposure pathways or routes to internal dose remains challenging. This study introduced the internal allocation factor (IAF) for 319 pesticides to investigate the impact of different exposure pathways and routes on chemical distribution within the human body. The IAFs can be calculated from various exposure sources (or pathways), routes, and biological samples. Analysis of different exposure sources revealed that crop exposure generally had the lowest IAF in organs and tissues, indicating a high contribution to the internal dose. The median IAF values for crop exposure in blood, liver, lung, kidney, fat, and muscle were all around 1.05. For three exposure routes of soil pesticide, the results found that IAF values for oral and dermal exposure routes were significantly lower than those for inhalation exposure. When the pesticide concentrations in biological samples are known, IAF can be utilized to back-calculate the pesticide levels in other organs and tissues. The results show that under a single exposure route, the concentration factor varies greatly between organs or tissues due to differences in compositions of human tissues (e.g., water and lipid contents) and pesticide properties (e.g., hydrophilicity and lipophilicity).