Comparing Polarography and Flame Atomic Absorption Methods in Determining Lead
and Chromium Concentrations in Sewage Sludge Treated Agriculture Fields

Amy Blankinship
School of Science & Natural Resources
April 19, 1997


Abstract

Municipal sewage and wastewater sludge has been applied to agriculture fields in the United
States since the 1970's This sludge is high in organic matter and other nutrients such as nitrogen
and phosphorous which are essential for crop growth and this makes it an alternative to
commercial fertilizer for agriculture fields The sewage sludge also contains other harmful
components such as heavy metals which can accumulate on the soil and be taken up by plants
and animals. Because of the harmful effects of metal loadings onto agriculture fields, a study
was conducted on agriculture fields in Bruce Township, Sault Ste. Marie, MI in which
wastewater sludge is being applied to these fields. The study was to determine the lead and
chromium concentrations in the fields as they varied with time of application and with depth.
Flame atomic absorption was the method used to analyze the samples. This research was to
determine the lead and chromium concentrations ofthe same samples using polarographic
analysis. It also compared the metal concentrations determined using polarography to the
concentrations obtained using flame atomic absorption. Four fields, each which received only
one application of sewage sludge for a specific year, and one control field were sampled. The
of application were from 1993-96. Samples were taken at depths of 0-15 cm and 15-30
cm. The soil samples were extracted using 4M nitric acid, and were analyzed using the EG&G
polarographic analyzer. The ANOVA test at 95% confidence interval showed no significant
difference for the lead concentrations between the fields and between the depths within a field
using polarographic analysis. A two-tailed paired t-test at a 95% confidence interval showed a
significant difference in the lead concentrations determined by polarography and flame atomic
absorption. Nitric acid interfered with the analysis of the samples when using polarography
which could account for the difference in the concentrations of lead between the two methods.
Methods such as ion-exchange could be used to diminish the interference of the nitric acid.


Selected References.

Emench W.E, L.J. Lund A.L. Page, & A.C. Chang. 1982. Movement of heavy metals in
sewage sludge treated soils. J Enviroyt. Qual. 11:174-178.

Pierce F.J., RH. Dowdy, & O.F. Grigal. 1982. Concentrations of6 trace metals in some major
Minnesota soil series. J Environ. Qual. 11:416-422.