Potentially toxic elements (PTEs) originating from wide variety of industrial and domestic sources enter wastewater and are concentrated in sewage sludge during water treatment. Controls, in the form of codes of practice and legislation, are in place in most developed countries to prevent the accumulation of damaging concentrations of PTEs in agricultural crops and soils. However, these controls fail to consider crop plants as vectors for PTE transfer into the arthropod fauna of agri-ecosystems. This study tests the hypothesis that plants may have an important role in mediating metal transfer to higher trophic levels in the agro-ecosystem.

Field plots were amended with sewage sludge at six rates between 0 and 80 t(ds) ha^-1 and three years later field peas were sown. The uptake and partitioning of Cd and Zn, between root, shoot and seedpods was determined in pea plants. The concentrations of metals were determined in aphids harvested from the pea shoots.

Uptake of metals by pea plants was related to the concentration in the soil; however, there was differential transfer through the components of the plant, depending on soil metal levels. Transfer of Zn from peas to aphids resulted in a doubling of concentration in aphid tissue. In contrast, Cd levels in aphids were lower than in the pea shoots on which they were feeding. These results support a hypothesis that plants are important in mediating metal transfer.