Toxicity tests have taken on increased importance after scientists realized that many substances are toxic to living things at levels below chemical detection limits and that there are no methods to analyze for many toxic substances. The Biology Laboratory conducts an array of toxicity bioassays. A toxicity bioassay may be run as a screening test, where the toxicity of a sample is compared to that of a control water, or as a definitive test, where several portions of the sample are diluted with varying amounts of the control water and their results compared to the control water. The screening tests indicate whether toxicity is present in the sample. The definitive tests indicate the amount of toxicity presented by the sample. Additionally, the results of a toxicity bioassay may be measured as either an acute response such as mortality or a chronic response such as growth or reproductive effects.

Samples of wastewater discharges are tested for compliance with limits established by permits. Tests for toxicity are also conducted in surface or ground waters during other investigations, including acute and chronic bioassays of both fresh water and marine fish, invertebrates, and algae. The biology lab can conduct on-site flow-through bioassays with its mobile laboratory. The Microtox procedures are sometimes used to measure the effects of toxicants on bacteria.

Toxicity Identification Evaluations (TIE's) involve a complex series of procedures in which an effluent is physically or chemically manipulated and toxicity tests are performed on each fraction. The results help identify the causes of persistent toxicity in discharges, and allow the facility to take appropriate action to alleviate whatever is causing the toxicity. To fully identify causes of toxicity, the TIE protocol requires that toxicity testing be carried out in close cooperation with substantial analytical chemistry support. To this end, the biology laboratory works closely with the FDEP chemistry laboratory, located in the same building.

Toxicity testing carried out in the Biology Laboratory includes:

Acute toxicity bioassays:

Chronic toxicity bioassays:

The Standard Operating Procedures used in preparation for and conducting these tests can be viewed or downloaded from the Biology Section SOPs. Summaries of toxicity bioassay reports are also available.