Research Areas > Contaminants > Toxicity Assessment and Identification > Background: TIEs

Background: Toxicity Identification Evaluation

It is often not enough to simply know that a sample is toxic; it is important to know what particular chemical(s) within the sample is causing toxicity. One of the critical steps in many management actions is to identify specific chemicals of concern. For example, once a water body has been determined to have impaired water quality due to chemical contamination, the causes of the impairment must be determined so that regulators can determine the contaminant load reductions needed to restore water quality.

A Toxicity Identification Evaluation (TIE) is a series of laboratory procedures used to identify the probable causes of toxicity in a sample of water or sediment. This process involves chemically sequestering specific contaminants or otherwise rendering them nontoxic and then retesting the sample to determine if a change in toxicity has occurred. For example, cationic metals can be chelated in an aqueous sample through the addition of EDTA. A typical process for treating and testing an aqueous sample is shown in Figure 1.

The TIE process is organized into three phases: Characterization (Phase I), Identification (Phase II), and Confirmation (Phase III). The purpose of a Phase I TIE is to determine which broad classes (i.e., metals or nonpolar organic compounds) of chemicals are responsible for toxicity. The process shown in Figure 1 is typical of a Phase I TIE for marine water samples. In a Phase II TIE the chemical(s) responsible are further narrowed by fractionating the sample, testing the fractions for toxicity, and then using analytical chemistry to identify the compounds present in the toxic fractions. In Phase III, the chemical cause is verified through add backs of removed constituents and spiking experiments.

Procedures are available for conducting TIEs on both water and sediment samples. The water procedures are well-established and have been used successfully in both fresh- and sea-water matrices for many years. The methods used on sediment are less developed and not as commonly used. The various TIE treatments that are commonly used at SCCWRP are shown in Table 1. Note that some of the treatments can be used in both aqueous and solid phase testing. SCCWRP has conducted TIEs on both aqueous and solid phase samples from a variety locations including: stormwater from San Diego urban creeks, and sediment and porewater from Newport Bay and the Ballona Creek estuary. The development and improvement of sediment TIE methods is an active field of research by the SCCWRP Toxicology Department.