Polychlorinated dioxins, dibenzofurans (PCDD/PCDF) and polychlorinated biphenyls (PCBs), are persistent organic pollutants (POPs) that bioaccumulate in lipids and may enter the food chain through animal products. Recently, Polish authorities discovered a free range farm whose eggs exceeded national standards for dioxin contamination two-fold. Piskorska-Pliszczynska et al.1 evaluated samples from that farm to determine the likely source of the dioxin exposure and to quantify the bioaccumulation of PCDD/Fs and PCBs in the tissues and eggs of the affected hens. They took specimens from the commercial feed and the soil of the free range areas. A veterinarian also performed necropsies and sampled muscle, abdominal fat, liver tissue, ovarian follicles, and whole eggs present in the oviducts. The researchers identified 35 PCDD/F and PCB congeners of interest, including dioxin-like polychlorinated biphenyls (DL-PCBs) and non-dioxin-like polychlorinated biphenyls (NDL-PCBs), using gas chromatography coupled with high-resolution mass spectrometry (Thermo Scientific) to analyze the samples. The free range egg samples contained a total PCDD/F and DL-PCB concentration of 12.55 ±2.37 pg/g, which exceeded the limit of 6 pg/g. The aggregate egg sample presented a high toxic equivalency (TEQ) for PCDD/F congeners (12.39 ±2.03 pg/g) and low TEQ values for both DL-PCBs (0.17 ±0.03 pg/g) and NDL-PCBs (1.12 ±0.25 ng/g of fat). The commercial feed samples were below the limit (1.50 ng/kg) at 0.07 ±0.01 ng/kg. NDL-PCB levels were also low at 0.04 ±0.01 μg/kg. Piskorska-Pliszczynska et al. assert that these measurements imply that commercial feed was not the source of dioxin contamination. The soil samples presented values of 28.96 ±4.85 pg/g for PCDD/Fs and 11.46 ±1.92 pg/g for DL-PCBs. The researchers found trace quantities of NDL-PCBs. The PCDD/F profiles of the soil samples, contaminated eggs, and tissue samples were very similar and suggest a link between soil ingestion and dioxin contamination. The researchers note that the hens’ soil consumption could result in daily dioxin intakes of 58-869 pg for the first free range area and 23-343 pg for the second area. The hens appeared malnourished, despite access to feed, and demonstrated a high load of ectoparasites, indicating weakened immune systems. Analysis revealed unacceptable dioxin concentrations in all tissue samples and specific bioaccumulation in liver samples. The birds with access to the most contaminated soil presented liver PCDD/F levels that were twice as high as the other samples from the same bird. However, the PCDD/F profiles varied among hens based on behavioral factors and uneven distribution of the soil contaminants. They theorize that the likely sources of soil contamination were uncontrolled waste-burning at neighboring farms and the proximity of an industrial plant with unknown combustion processes. Overall, Piskorska-Pliszczynska et al. determined that laying hens allowed to forage in soil with dioxin contamination of 10-20 ppt present a public health threat and that even trace levels of lipid-soluble POPs may contaminate the eggs and meat of free range fowl. They called for further studies on uptake and bioaccumulation npatterns of PCDD/F and PCB congeners. They also recommend increased monitoring of soil dioxin levels and point to the lack of an enforceable maximum standard as a barrier to this endeavor. References
- Piskorska-Pliszczynska, J. et al. (2014) ‘Soil as a source of dioxin contamination in eggs from free-range hens on a Polish farm.’ Science of the Total Environment 466–467, pp. 447–454
Do you work in this type of environment? How concerned are you about soil contamination?