In 1987, a multidisciplinary dairy project was initiated at the Mahoning County Farm in Canfield, Ohio. The principal objectives of this project were to evaluate the feasibility of seasonal and rotational grazing programs in Ohio. Paddocks were established over 42 acres which were subdivided using electrified fencing. Twenty-five percent of this pasture land had a previous history of use as orchards (Figure 11.1). These orchards were managed in typical fashion utilizing a broad range of pesticides which were legally applied at the time of use. At the beginning of this study, there were 33 pesticide formulations, including organochlorine formulations, stored on the Mahoning Farm premises. The latter are extremely stable compounds and, when applied to crops or orchards, persist in the soil and environment for many years.
Early in 1987, a series of soil cores was obtained for pesticide analysis. These cores, in conjunction with aerial photographs, determined the boundaries of the contaminated soils and indicated the concentrations of pesticides present. The organochlorine pesticides detected were heptachlor, lindane, DDT, and its metabolites DDE and DDD. These metabolites are derivatives of the chemical DDT in the soil. Concentrations of heptachlor and lindane were infrequent and near the limit of analytical sensitivity, so these were not included in our continuing studies. The DDT and its breakdown products were primarily within the boundaries of the old orchards, as indicated on the aerial photographs. Drift from the spraying operations or water run-off did contaminate six locations of immediately adjoining pastures with concentrations which were less than .03 ,micro g/g (micro g/g = parts per million). Despite the occurrence of plowing of these old orchard sites, the majority of DDT and DDE residues were located near the soil surface. The average concentrations of DDT at the surface and at 14-16 cm of depth were 1.90 + .27 and .41 + .01 micro g/g, respectively. Concentrations of the residues varied considerably from location to location, with concentrations ranging from none detected to nearly 4 micro g/g.
Pesticide formulations which contained the heavy metals lead, arsenic, and copper also were used on these orchard plots. Concentrations of these three metals were detected, not only within the boundaries of the orchard land, but also in adjacent areas which were down-wind and down-slope (Table 11.1). It was clear from these samples that the heavy metals were far more mobile by percolation, run-off, and/or overspray than were the organochlorine pesticides.
At the onset of the dairy project, all cows were sampled to confirm that their milk was free of organochlorine pesticides or other halogenated hydrocarbons such as poly-chlorinated biphenyls. Concentrations of heavy metals were not determined in the cattle.
During the next three years, samples of milk and body fat were collected from these cows to determine whether the organochlorine residues known to be present in the soil would contaminate the livestock intensively grazing these pastures.
Residue determinations during the first year of study clearly pointed out that these soil residues from DDT represented a source of pesticides which would contaminate livestock. The DDE concentration in individual milk fat samples ranged from none detected to .356 micro g/g. Residues exceeded .12 micro g/g in 11 of the 30 cows. During this year, cows were sampled on days 3, 30, 60, 120, and 180 of lactation which did not necessarily relate to exposures to orchard paddocks.'
During the next two years, the sampling protocol was changed so that the residue uptake by cows could be related to particular paddocks. During year two, each cow had milk samples collected two days after she was removed from a contaminated pasture. In the third year, residues were monitored by milk collected from a pool of all cows at approximately two day intervals.
Table 11.2 shows the concentrations of DDE in the milk fat of cows before and two days following grazing of the contaminated orchard paddocks. The two-day withdrawal after exposure allowed the milk fat concentration to represent the equilibrium between body fat and milk fat, thus excluding the amount of residue available from recently-eaten forage. This phase of the study clearly showed that all cows were exposed to similar amounts of pesticide residue when on a particular paddock, but it did not explain why those concentrations varied even when cows were placed back on the same paddock.
The concentrations of DDE in the milk fat during the third year are shown in Figure 11.2. These represented the residue concentrations in the pooled milk. The cows were limited from continued access to the most contaminated plots during this year. Residues remained well below regulatory tolerances.
The majority of the scientific literature dealing with the translocation of pesticides in plants suggests that the residues of DDT and its metabolites DDE and DDD do not translocate through the roots to other parts of the plant. However, the concentrations of residue appearing in the cows were sufficiently high that, based on the equation [DDE, micro g/g]milk fat = .28(daily dose) 82, it seemed unlikely that soil consumption was the sole source of residue. When the concentration of DDE in milk fat reached .3 ,micro g/g, then the cows were consuming approximately 1.1 mg of pesticide per day. Similarly, approximately .28 mg/day would be required to sustain a milk fat concentration of .1 ,micro g/g. If soil was the sole source of pesticides, cows would have had to be consuming between 1 and 2 kg of soil per day - an unlikely possibility. Therefore, grass was suspected to be a carrier medium for the residues from the soil to the cows.