Transfer of Cl from herbage into tissues and milk products of dairy cattle and pigs

Cl-36 is an important component of nuclear waste. The concentrations of stable chlorine (Cl) in pig and cow tissues were measured to provide information which can be used to parameterize models of 36Cl transfer into agricultural animals. The concentration of stable Cl in cows’ milk was 1.0 ± 0.2 g L–1, in cow muscle it was 0.7 ± 0.2 g kg–1 wet mass (wm) and in pig muscle 0.4 ± 0.1 g kg–1 wm. The concentration of stable Cl in cow and pig liver was 0.9 ± 0.3 g kg–1 wm, which was about two-fold higher than that in the kidney and lung. Due to homeostatic control, stable Cl concentrations in animal tissues are not related to the amount ingested daily in herbage at intake rates in the normal physiological range of up to 188 g day–1 for cows and up to 40 g day–1 for pigs. Therefore, the commonly used transfer coefficient is not suitable for use in quantifying the transfer of 36Cl to milk and meat. Since the metabolism of stable Cl and 36Cl in an animal’s body is identical, the average equilibrium ratios of 36Cl to stable Cl in the daily ration (36Cl (g kg–1)/ Cl (g kg–1)) and animal tissues will be the same. We therefore conclude that the average equilibrium Cl isotopic ratio in the dietary daily intake should be used to predict the contamination of meat and milk with 36Cl.