Heavy Metal Concentrations During Ten Years of Sludge Treatment to an Old-Field Community

Heavy metal concentrations were determined in three trophic levels of an old-field community treated for 10 consecutive years with sewage sludge. The study site consisted of sludge-treated, fertilizer-treated, and control plots. Cadmium concentrations were highest each year in soils, vegetation, meadow vole (Microtus pennsylvanicus Ord.) livers, and earthworms (Lumbricus rubellus Hoffmeister, L. terrestris L.) from sludge-treated plots. Mean Cd concentrations in sludge decreased from 59.0 mg kg⁻¹ in 1978 to 19.8 mg kg⁻¹ in 1987, whereas Cd concentrations in soil increased from 1.13 mg kg⁻¹ in 1979 to 1.94 mg kg⁻¹ in 1987. Plant species in sludge plots had significantly higher Cd concentration values than those collected from fertilizer or control plots. No yearly increase in Cd content was observed in meadow vole liver or kidney. Cadmium concentrations in earthworms were significantly greater in 1981 (139.2 mg kg⁻¹) than in 1987 (60.9 mg kg⁻¹). Copper concentrations were highest in soils, giant foxtail (Setaria faberii Hermm.), and earthworms from sludge-treated plots. Mean Cu concentrations in sludge ranged from 320.0 mg kg⁻¹ in 1978 to 380.6 mg kg⁻¹ in 1984. Copper concentrations in soil ranged from 14.7 mg kg⁻¹ in 1979 to 36.9 mg kg⁻¹ in 1986. Vegetation in sludge plots concentrated Cu less than vegetation in fertilizer or control plots. Cu concentrations in meadow vole liver decreased from 5.0 to 3.1 mg kg⁻¹ and in kidneys from 4.9 to 3.3 mg kg⁻¹ in 1978 and 1987, respectively. Copper concentration in earthworms ranged from 17.1 mg kg⁻¹ in 1981 to 23.0 mg kg⁻¹ in 1987. Although Pb concentrations in sludge declined from 473.0 mg kg⁻¹ in 1978 to 243.0 mg kg⁻¹ in 1987, mean Pb concentrations in soil increased from 19.0 mg kg⁻¹ in 1979 to 48.4 mg kg⁻¹ in 1986. However, only giant foxtail in sludge-treated plots significantly concentrated Pb. Mean Pb concentrations in earthworms ranged from 8.06 mg kg⁻¹ in 1986 to 16.8 mg kg⁻¹ in 1987. Mean Zn concentrations in sludge ranged from 865.8 mg kg⁻¹ in 1987 to 1281.0 mg kg⁻¹ in 1984. Zinc concentrations in soils increased from 52.4 mg kg⁻¹ in 1979 to 107.2 mg kg⁻¹ in 1987. Zinc concentrations varied substantially among plant species; mean Zn concentrations in 1987 ranged from 41.0 mg kg⁻¹ for Rubus frondosus Bigel. (a perennial) to 97.3 mg kg⁻¹ for giant foxtail (a summer annual). Zinc concentrations in earthworms decreased from 1218.5 mg kg⁻¹ in 1981 to 615.5 mg kg⁻¹ for 1987. The detritivore trophic level bioconcentrated heavy metals more than producer or primary consumer levels.