Lead Content Of Soil To Which Untreated Sewage Is Applied


DanaL. Sanford
School of Science and Natural Resources
Lake Superior State University
Sault Ste. Marie, Ml 49783



Abstract. A previous study conducted in Oakland, California revealed that land
application of untreated sewage caused lead levels in soil to increase to dangerous
amounts. There is concern that the lead from land application of sewage is causing soil
pollution and ground water contamination. Exposure to lead is hazardous and may cause
a variety of brain and nervous system damage. These health risks prompted the present
study of a 6 acre plot of land in Benzie County, Michigan which has been treated daily for
5 years with untreated sewage from a rural community. The object ofthis study was to
take soil samples from this plot of land and analyze the samples for lead content. A total
of 4O samples were gathered on July 25, 1996. Twenty from the sewage treated land and
twenty from an adjacent 6 acre plot of untreated land that would act as a control. The
samples were prepared by extracting the lead from the soil using a modified version of the
procedure by Williams et al (1984). The sample extracts were analyzed using Atomic
Absorption Spectrophotometry. A standard addition technique was used to account for
any interferences that may be present in the sample extracts. Out of the 40 samples, all
were well below the DNR's and HUD's approved limits of4OO ppm for lead in soil. In
addition, the DNR stated that soil gathered from a rural area should contain lead at or
below a value of 50 ppm. All 40 samples were also below this expected value. A Mann-
Whitney test of significance found no significant difference in lead concentrations between
the sewage treated field and the untreated field, and it was concluded that the sewage
treated land was not being polluted with lead.





Selected References


Williams, D.E., J. Vlarnis, A.H. Pukite, and J.E. Corey. 1984. Metal Movement in
Sludge-Treated Soils After Six Years of Sludge Addition: 1. Cadmium, Copper,
Lead, and Zinc. Soil Science 137: 351-359.

McBride, MB. 1995. Toxic Metal Accumulation From Agricultural Use ofSludge: Are
USEPA Regulations Protective? Journal ofEnvironmental Quality 24 : 5-18.