Declining levels of PCB, HCB and p,p'-DDE in adipose tissue from food producing bovines and swine in Sweden 1991-2004.

The official control programme for organochlorine (OC) contaminants in food producing animals in Sweden was used to study temporal and spatial trends of the polychlorinated biphenyl CB 153, hexachlorobenzene (HCB) and p,p'-DDE in adipose tissue from bovines and swine 1991-2004. Our results show that efforts to decrease OC contamination of animal feed and the environment have had a positive impact on the contamination of the animal production. OC concentrations declined significantly in almost all studied regions of Sweden. OC temporal trends were slower in bovines (6-8% per year) than in swine (10-12%). Power analyses showed that data from more than 10 years of sampling were needed for a detection of an annual OC level change of 5% in both species in the control programme, due to large within- and between-year variation in OC levels. CB 153 and p,p'-DDE levels were higher in southern than in northern Sweden. Levels decreased with age in milk cows, but not in young nulliparous cows (heifers) and bulls. Moreover, milk cows and bulls had significantly lower OC levels than heifers. Levels were not age-dependent among swine, but castrated male swine (barrows) had significantly lower OC levels than young female swine (gilts). Levels of the studied OCs are now in many cases below the LOQ of the analytical method used. Future time trend studies of these OCs thus depend on lowered LOQs in the control programme.