Soil lead levels in orchards and roadsides of Mission Peninsula, Michigan

The Pb content in orchard soils at Mission Peninsula, Michigan was determined to assess the impact of historical lead arsenate applications. Soil samples at 72 sites located in five orchards were collected at depths of 2-, 20-, 50-, and 100 cm. Atomic absorption spectroscopy was used to quantify Pb levels (mu g g(-1)). Mean surface Pb levels at individual orchards ranged from <1-136 mu g g(-1) and rapidly decreased with depth, to <1-5 mu g g(-1) at 100 cm. The impact of textural class and slope angle on Pb levels was also analyzed. Correlation coefficients linking Pb levels with textural class were weak, ranging from 0.21 to -0.07. Varying slope steepness and slope position within orchards failed to affect the spatial pattern of soil Pb. Soil Pb levels were also compared at 5 sites along local roads with varying levels of automobile traffic. Samples were collected 1 m from the roadside at the same depth intervals studied in orchards. Average daily traffic along the busiest roadsites ranged from 8200 to 16 000; these sites had Pb levels of 90-210 mu g g(-1). Such locales had Pb levels similar to the more intensively sprayed orchards.