The transfer of ⁷³As, ¹⁰⁹Cd and ²⁰³Hg to the milk and tissues of dairy cattle

Abstract

SU MMARYBy a variety of exposure routes it is possible that the toxic heavy metals cadmium, arsenic and mercury could enter the diet of farm animals and hence contaminate food products derived from those animals. Therefore, there is a need to be able to assess the likely levels of contamination in animal tissues if exposed to contaminated feed and also to estimate how rapidly an animal will decontaminate once the source of contamination is removed from the feed. The development of dynamic models to predict changes in the degree of heavy metal contamination in tissues of ruminants have been hindered by the lack of data on the transfer and excretion rates of these metals from tissues. A study is described during which dairy cows were given a single intraruminal administration of 109 Cd, 73 As and 203 Hg and measurements made of the subsequent concentrations of the radioisotopes in body tissues and milk. The resultant data were used to adapt previously developed compartment models describing the behaviour of the metals in sheep for use with dairy cows. Two changes were made to the sheep models : (i) a new excretion route was included to describe transfer to milk; (ii) the rate coefficients (with the exception of those involving gut absorption and transfer) were adjusted according to the ratio of the metabolic live-weights (live-weight (kg) 0 . 75 ) of the sheep to that of the cattle. The models predicted levels of the metals in the cattle tissues and milk reasonably well.

Radionuclide transfer to animal products: revised recommended transfer coefficient values

“…Beresford et al (1996Beresford et al ( , 1996c and Crout et al (2004) report data from single administration studies which they interpreted by fitting models to data for consecutive slaughter dates over a circa 1 year. Subsequent predictions of F f were made for differing periods of continuous administration; values incorporated into the database from these studies were the equilibrium or 1000 d predictions.…”

Gastrointestinal fractional absorption of radionuclides in adult domestic ruminants

“…For cadmium, the value in Table 1 is an A a estimate derived by Crout et al (2004) from a compartment model based on an experimental study with three lactating cows given a single oral administration of 109 CdCl 2 . Urine and faeces were retained for 7 days and the cows slaughtered after 28 days and tissues analysed; milk was sampled throughout the 28 day experimental period.…”

The transfer of radiocaesium to ewes through a breeding cycle – an illustration of the pitfalls of the transfer coefficient

“…The concept has also been adopted within some heavy metal food chain models (e.g. Fayers, 1994) although others have suggested that equilibrium transfer coefficients are inappropriate because of the long biological half-lives of some heavy metal elements (Beresford et al, 1999;Crout et al, 2004).…”