Toxicity testing is an important part of assessing the risk to biological organisms of existing and
new chemicals that are to be released to the environment, as well as those field soils that
potentially contain different forms of contaminants. Much of the information produced through
toxicity tests is used as part of risk assessments, in remediation plans, and in the development
of environmental quality criteria, standards, objectives, or guidelines. Different species are used
for terrestrial toxicity testing, including those belonging to the major groups: plant, collembola,
and earthworm. Many soils received for toxicity testing are difficult to work with and are
considered to be ‘non-ideal’ for the various organisms used for testing; these sub-optimal soils
present challenges for assessors. Often, the structure of these soils is not acceptable for the
biological organisms because they do not support survival, growth, and/or reproduction. Clayey
soils typically have a high bulk density, poor drainage, and are prone to compaction. Soils that
have a high sand component, low moisture retention, and low organic matter content are also
sub-optimal. From our experience, earthworms seem especially sensitive to the structure and
condition of the test soils and, although earthworms can survive in soil with little structure, they
rarely reproduce. Since earthworms inhabit soils, they need to be able to move through the soil
to live. In tests where earthworm survival, reproduction, and growth were inhibited, it was
unclear whether the observed responses were due to the contaminants in the soil or to the
structure and characteristics of the soil being tested.
The purpose of this literature review was to describe the various soil conditioners that have
been used to improve the characteristics and structure of soil, and to identify potentially
appropriate soil conditioners to be used to improve the structure of soils for use in toxicity tests
with biological organisms, especially earthworms. The second part of this project involves
comparative laboratory testing of the selected soil conditioners, to determine the conditioner(s)
most appropriate for use in toxicity testing with the “structurally-challenged” soils.
