Effects of zinc-smelter emissions on forest soil microflora

Abstract

Within 2 km of a zinc (Zn) smelter in Palmerton, Pennsylvania, near the Lehigh Water Gap, up to 13.5% Zn by weight has been measured in the O 2 horizon of the soil, and up to 8% Zn in the A 1 horizon. The total numbers of bacteria, actinomycetes, and fungi (measured by dilution plate counts) were greatly reduced in the most severely Zn-contaminated soils compared with control soils. The reduction of microbial populations may be a partial cause of the decreased rate of litter decomposition at Lehigh Gap.Growth of most bacteria from control sites was reduced by 100 to 200 μM Zn, most actinomycetes by 100 μM Zn, and most fungi by 100 to 1000 μM Zn in thin-Pablum extract agar (TPab). All the tested actinomycetes and non-spore-forming bacteria isolated from Zn-contaminated Lehigh Gap soils were Zn-tolerant, growing normally in media containing 600-2000 μM Zn. Most fungi, regardless of source, were capable of at least 50% of normal growth at 700 μM Zn. Zinc-tolerant bacteria, actinomycetes, and fungi were readily isolated from low-Zn soils, suggesting that selection for Zn tolerance may proceed rapidly.Acidophilic Mortierella species have been selectively eliminated near the smelter, apparently because of elevated soil pH. Peyronellaea glomerata (Corda) Goidanich and Coniothyrium spp. were found only in the high-Zn soils.