This is because paddock soil levels are not a good indicator of OC levels in cattle grazing the pasture. There are a variety of other factors such as 'hot spots', season, pasture variety and condition, soil type and animal condition that affect animal levels. The level to which plants become contaminated depends on the type of soil in which they are grown. Plants grown on soils with a high organic content are less likely to have high OC residues than plants grown on sandy soils. This is because OCs are strongly bound to the organic content of soils which means transfer of OCs from the soil to the plant is at a lower rate.
Organic soils are less prone to being splashed onto plants.
However, when drought occurs, organic soils can contaminate pasture plants due to the dry dusty conditions. Residues can also contaminate pasture plants and fodder crops by uptake of these chemicals via the roots. The level of residue depends on the soil, season, plant type and relative stage of plant growth but is generally very small compared to plant soil contamination . Taller plants generally tend to have less OCs than smaller ones because the tops of plants contain less residues than the lower sections. In addition, taller plants tend to shed their lower leaves which reduces the contamination load.