Domestic chickens as a biomarker for trace element exposures in home environments

Accumulation of potentially toxic heavy metals at elevated concentrations constitute one of the threats to the natural environment, ecosystems and the health of living organisms. In this study, the prevalence of trace metal (As, Cd, Pb, Cr, Cu, Ni and Zn) exposure in backyard chickens via multiple exposure routes (soil, water, feed) was determined to better understand risks to the chicken and implications for egg production in relation to human consumption. Sixty-nine domestic chickens from 55 Sydney urban backyards were tested for their Pb concentrations using a LeadCare Plus™ Analyzer with their matched eggs analysed for Pb and other trace elements using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Corresponding soil, drinking water and feed were also sampled and subjected to a combination of ICP-MS and portable X-ray fluorescence spectrometry (pXRF) analysis. A significant association is observed between garden soil concentration and domestic chickens and their eggs and enables a broader determination of risk by using existing soil trace element data to domestic chicken. In addition, age of homes, distance to CBD and age of birds were also correlated with higher Pb in chicken blood and egg.

As maximum limit has not been assigned to lead and other elements in chicken egg in the Australian New Zealand Food Standards Code, the relevant Health Based Guidance Values (HBGVs) were used as a benchmark dose to compare the dietary exposure assessment values from chicken eggs to assess the food safety risk through the consumption of domestic eggs. The study also showed that the Pb and other residual concentrations of metals (As, Cd, Cr, Cu and Zn) in 9 different commercial free-range farm eggs had significantly lower mean concentrations. The health risk for consumers was assessed for two age categories of consumers (children:2-6 years, adult >18 years) by calculating the estimated daily intake (EDI), the target hazard quotient (THQ) and the cancer risk (CR) for each contaminant and showed a carcinogenic and non-carcinogenic risk for children with an exceeding elevated metal concentration (As, Cd, Pb and Zn) through the consumption of backyard chicken eggs. This assessment can be used to make recommendation for risk assessment and for soil screening and clean up values in order to ensure chicken safety and mitigate human exposures through consumption of home-grown chicken products.