Toxicity and fate in the terrestrial environment

For the past 30 years the focus of regulatory environmental risk assessment, has been largely on the aquatic compartment. More recently, legislation has required work to be carried out to assess toxicity of substances in soils as well. For many tests with soil, the test chemical is dissolved, or emulsified in deionized water and then thoroughly mixed with artificial soil. A contaminated soil sample can also be tested by diluting with artificial soil, and then by exposing the organisms, whether animals or plants.

It is very important to carefully consider the content of organic carbon in both soil and sediment. Organic carbon can influence organism health, and can also affect test substance bioavailability. In many tests, it is necessary to allow equilibration of the test substance spiked to the soil or sediment for several days to mimic environmentally relevant aging conditions.

Examples of organisms commonly used in terrestrial toxicity tests
  • Plants (e.g. lettuce, radish, rye grass)
  • Worms (earthworms, oligochaetes)
  • Collembola

Ecotoxicity assessment relies on a number of
defined tests on sediments and soil

Sediment toxicity tests
Sediment tests are primarily performed on invertebrates which will either burrow into, or ingest sediment, and as with aquatic tests, employ standard test protocols developed for a wide variety of different species including amphipods, insects, worms and oligochaetes. Control (clean artificial or natural) sediment can be spiked with a test chemical, or a contaminated natural sediment can be tested.

Exposures range from 10 to 30 days, with renewal of the overlying water during extended periods. Endpoints evaluated in sediment tests can consist of survival (LC50), growth and development (EC50), and reproduction (egg production and number of young produced).
 
Terrestrial toxicity tests
As with aquatic toxicity tests, a variety of species have been identified which are used as standard test organisms in terrestrial studies. These studies are focused on plants and animals which live in soil and also on birds (avian). OECD guidelines have been developed for acute toxicity studies using plants (OECD 208), earthworms (OECD 207), and birds (OECD 205). The plant toxicity studies allow the use of a very long list of species, most of which are grains or vegetables of commercial value.

The acute studies relate the concentration of the chemical or diet to the mortality of the test organism or to germination in the case of plants. Chronic guidelines for tests with birds, earthworms and the collembolan Folsomia candida have also been defined. These tests examine the effect of the chemical upon reproduction.

Page glossary

  • Acute
  • Acute Toxicity
  • Avian
  • Bioavailability
  • Chronic
  • EC50
  • Ecotoxicity
  • Effect
  • LC50
  • OECD
  • Risk
  • Risk Assessment
  • Substance
  • Toxicity