Mechanisms of movement of organochlorine pesticides from soils to cows via forages.

When cattle were allowed to graze land previously used as orchards, residues of DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] were detectable in milk fat and adipose tissues. Concentrations of DDE exceeded .3 micrograms/g at times. Concentrations of DDE in adipose tissue were similar to those in milk fat at the beginning of lactation; residues in first lactation cows were approximately three times higher than in multiparous cows that were grazing similarly. Based on the equation [DDE, micrograms/g]milk fat = .28 (daily dose, mg).82, consumption of soil was likely not the sole source of residue when soil concentrations of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane], DDE, and DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] ranged from non-detected to 3.6, 2.1, and .655 micrograms/g, respectively. Grass appeared to be the likely source. Four plots were located on three orchard locations and one control location. Grasses in subplots were harvested at 2-, 4-, or 6-wk intervals during the 18-wk study. Grasses were extracted differentially to determine DDT and DDE residues adhering to the plant surface and those associated with plant tissue. Surface residue was not significant. The DDE averaged between .01 and .11 micrograms/g in dry grass tissues. Differences between residues in grasses among plots were associated with soil residue concentrations. Concentrations of DDE were not associated with air or soil temperature, relative humidity, solar radiation, or dry biomass harvested. Precipitation increased the volatilization of residues from soil and deposition in 2- and 4-wk grass samples.(ABSTRACT TRUNCATED AT 400 WORDS)