Free-range eggs dioxin contamination assessment: comparison between a simple model and in situ measurements to determine a maximum egg frequency consumption

Abstract

Dioxins (polychlorinated dibenzodioxins - PCDDs) and furans (polychlorinated dibenzofurans - PCDFs), are a family of aromatic organochlorine molecules whose primary origin of their emission is industrial processes requiring a combustion process. These compounds are very lipophilic, stable and not very biodegradable. These persistent organic pollutants accumulate in fatty tissue. For this reason, food is one of the main source of exposure to PCDD/Fs in our daily environment. Following a large PCDD/Fs soil contamination in Lausanne (Switzerland), a first report evaluated the risk of different exposure scenarios. Poultry houses on contaminated soil represent a risk of contamination by ingestion of PCDD/Fs contaminated eggs. Chickens peck on contaminated land ingest soil. The PCDD/Fs absorbed are found in their fat mass and are eliminated through the eggs. The objective of the study was to evaluate the expected concentrations in eggs as a function of the concentrations in the soil and express recommendation on the frequency of ingestion to remain below the acceptable daily intake. We fitted a PCDD/Fs toxicokinetic model in hens to evaluate the sensitivity of the different parameters. In order to validate the model, we sampled eggs and soil from five chicken houses in the contaminated area. The PCDD/Fs in eggs were extracted by liquid-liquid extraction and quantified by gas chromatography high resolution mass spectrometry. The PCDD/Fs from the soil were extracted using an Accelerated Solvent Extraction and then quantify by gas chromatography high resolution mass spectrometry. The results from the model were compared to the measured concentrations. The model is conservative since there is a tendency to overestimate the real concentrations. A rapid elimination phase during the first days is followed by first order kinetics. Overall, the half-life is 50 days. After 200 days, an equilibrium is reached and the concentrations in the eggs are stable. The parameters that influence the concentrations measured in the eggs are: the soil concentration, the geophagy (amount of soil ingested by the hen during pecking), the age of the hen (or its duration on the contaminated soil) and the egg laying efficiency. The geophagy parameter is the most difficult to predict. In order to limit health risks, we would recommend avoiding eggs from hens if they are pecking on soil above 50 ng Toxic Equivalent (TEQ)/kg soil. Below this concentration, it is recommended to ensure a good vegetation cover to limit geophagy and depending on the soil concentration to reduce the frequency of egg consumption