Factors controlling the lead content of a pasture grass

Abstract

The rate of deposition of atmospheric lead to moss bags shows a marked seasonal variation, both adjacent to a major road and at a rural background site. Deposition during winter months can be up to tenfold greater than in the summer. Atmospheric lead is the major source of lead to pasture at all sites in the winter months. Changes in the deposition rate of lead to moss bags over the winter period produce a corresponding variation in the pasture lead content. Rainfall has little effect upon grass lead levels. In summer, soil is the major source of lead to pasture grass except within 50 m of the M6 motorway, where the deposition rate of atmospheric lead is elevated in comparison with background sites. Plant growth processes determine a maximum level of lead in pasture for a given rate of deposition. This is a consequence of the limited lifespan of individual leaves and tillers which results in a loss of lead from the plant canopy to the soil.