Understanding Aquatic Toxicity Testing

The information below is a quick resource for Hydrosphere Research NPDES permit holders required to perform effluent toxicity testing or for those utilizing toxicity testing as part of a toxicity reduction program. Please note this is a just short synopsis. Click here to download the complete Understanding Aquatic Toxicity Testing information PDF.
(206 Kb PDF document)

Toxicity refers to the potential for a substance to produce an adverse or harmful effect on a living organism. A toxicant is an agent (e.g., whole effluent discharge) that can produce an adverse effect in a biological system, seriously damaging its structure or function or causing death. The adverse response may be defined in terms of a measurement that is outside the "normal" range for healthy organisms, such as abnormal mortality, reproduction or growth.

Toxicity tests determine the level of toxicity, if any, present in an effluent and the duration of exposure required for the toxicity to be expressed as adverse effects.

Organisms are exposed in test chambers to various concentrations of the effluent. The criteria for effects, such as mortality and reproduction, are evaluated by comparing those organisms exposed to different dilutions of the effluent with those organisms (controls) exposed only to nontoxic dilution water.

Toxicity test protocols typically specify the exposure of test organisms to fixed concentrations of whole effluent for a defined time period. Species selection (test organism) is one element that defines a specific toxicity testing procedure. Test species are selected based upon the ease of laboratory culture, the availability of adequate background information such as its physiology, genetics, and behavior and sensitivity to a wide range of toxicants.

Types of Toxicity Tests

Acute Toxicity Tests
Acute toxicity tests determine whether some concentration of test material or effluent will produce an adverse effect on a group of test organisms during a short-term exposure under controlled conditions.

Chronic Toxicity Tests
Chronic toxicity tests allow evaluation of adverse effects of an effluent under conditions of long-term exposure. Lengthening the test duration to include one or more complete life cycles or performing the test during a sensitive life stage allows the detection of more subtle adverse effects, such as reduction in growth and reproduction. Evaluation of these effects from long-term exposure to the effluent can provide a direct estimate of the effect threshold of the toxicant. During life cycle tests with several species of fish and invertebrates, certain developmental stages have consistently been shown to be more sensitive than others. Use of shorter tests with the early developmental stages can also predict chronic toxicity. These methods have been developed to provide quicker and less costly ways to measure chronic toxicity to aquatic organisms.

Presenting and interpreting acute and chronic toxicity test results requires the use of statistical analysis. Supporting statistics are used to evaluate the level of confidence that may be associated with the test results. At Hydrosphere Research, we ensure you receive accurate and timely data explained and prepared to meet all of your needs.

For much more detailed information on aquatic toxicity testing and how it works, please download and review the Understanding Toxicity Testing PDF. (206 Kb PDF document)