LAND APPLICATION OF INDUSTRIAL WASTES:
EFFECTS OF METALS ON SOIL BIOTA
Edward F. Neuhauser, Research Associate
Michael R. Malecki. Research Support Specialist
Raymond C. Loehr, Professor
Department of Agricultural Engineering
Cornell University
Ithaca, New York 14853
This study describes a system that is being developed to evaluate the effects of metals
on soil biota. With the increasing emphasis of land application of waste materials, methods
to assess the impact of these materials on the soil biota are needed. Knowledge about factors
that affect the soil biota is important since soil biota are responsible for much of the chemical breakdown that occurs when waste materials are applied to soils.
Metals are potentially toxic compounds which are contained in some waste materials
and were chosen for the initial screening of the methods described in this chapter. The
methods have been able to identify the toxicity of metals added to soils and are now being
evaluated with other chemicals, such as the organic priority pollutants.
Earthworms were chosen as the test animal because in the reported study they are a
major component of the soil fauna and are amenable to laboratory use. In addition, one
can identify earthworm growth and reproductive effects reasonably rapidly and a great
deal is known about their biology. The species of worm used in this study, Eisenia foetida,
was selected because a large amount of information is known about its growth [11, reproduction [2] and use in waste management systems [3).
METHODS AND MATERIALS
The worms used in these studies were grown in the authors' laboratory on a locally
obtained organic substrate. Cultures were maintained at room temperature (21-24°C),
with cocoons being harvested every 2 weeks. A constant supply of cocoons provided young
worms, <2 weeks old, that were used in all experiments. Young worms used in screening
tests give much more consistent results than adult worms of unknown age. Short-term
studies (8 weeks) were designed to provide information on survival and growth rates while
long-term studies (20 weeks) were designed to provide information on reproduction. Five
metals were used in the initial tests. The six chemical forms of each metal used covered a
broad range of solubility and represented chemical forms likely to be found in the soil.
The metals used in this study and their solubilities are noted in Table I.
The metal to be tested was mixed with a known amount of the organic substrate to
achieve the desired metal concentration on a ppm dry weight basis. The growth studies
used 20 g of the substrate metal-mixture placed on 30 g of screened soil in a 20- x 100-mm
petri dish. Five dishes per concentration were tested in each evaluation, with two worms,
<10 mg, in each dish. Controls consisted of substrate without the addition of metal. The
worms were checked for survival and weight gains at four, six and eight weeks and refed at
four and six weeks. Cocoons produced during the last four weeks of the growth experiments were counted to give preliminary estimates of reproductive effects.
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