WHOLE EFFLUENT TOXICITY
Throughout the United States, literally billions of gallons of treated wastewater re-enter our waterways from industrial and municipal water treatment plants. Unfortunately, even state-of- the-art wastewater treatment does not completely remove all chemicals and foreign materials present in the water.
To protect the environment and to ensure water treatment is performed as effectively as possible, federal agencies such as the Environmental Protection Agency, state agencies, and local governments require strict monitoring of treated wastewater being released back into the environment.
Whole Effluent Toxicity (WET) provides critical laboratory data for industrial and municipal wastewater treatment plants that have been identified as having a reasonable potential to adversely impact the waterway where their effluent water is discharged. Whole Effluent Toxicity verifies that effluent discharges into lakes, streams and rivers are within the parameters of environmental regulatory discharge permits and that the effluent does not contain toxins that can have harmful, even devastating effects on the receiving stream ecosystem.
Wastewater (influent) entering treatment plants can originate from many diverse sources and contain the waste by-products of multiple industrial processes. The mixing of influent flows can result in chemical compounds that are nearly limitless in number and per- haps very toxic if released into a waterway ecosystem. While traditional analytical laboratory procedures are beneficial in screening for the presence of many chemical compounds, these procedures do not determine the toxic effects on living organisms.
In addition, there are simply too many chemical combinations possible to efficiently use traditional analytical techniques. Organisms commonly used for laboratory Whole Effluent Toxicity tests are Pimephales promelas (fathead minnow), Ceriodaphnia dubia (water flea) and Daphnia magna (water flea). Test protocols are divided into two classifications: acute and chronic toxicity testing. Test parameters for Whole Effluent Toxicity testing are normally specified in “discharge monitoring permits”.
Typical permits requiring Whole Effluent Toxicity meet one or both of the following criteria:
1. Discharging more than one million gallons of effluent per day (classified as a major facility);
2. Wastewater discharges that have a reasonable potential to cause or contribute to water quality degradation of the receiving stream.
Acute toxicity tests measure the survival of test organisms exposed to a series of dilution concentrations of the effluent sample over a period of one to four days. By using a series of effluent dilutions, the concentration level at which the effluent becomes toxic is more easily identified. Chronic toxicity tests use sub-lethal concentrations of the effluent sample and tracks survival and growth of Pimephales promelas and / or survival and reproduction of Ceriodaphnia dubia.
Control group studies are done in conjunction with effluent dilution studies using synthetic water. When calculating study results, measurements such as growth rate and survival percentage for the test group (effluent dilution) verses the control group (synthetic water) are compared using computerized statistical programs.
McCoy & McCoy Laboratories, Inc. is one of the leading laboratories in this testing field. With over twenty years of experience and state-of-the-art equipment our laboratory can help you with maintain compliance with sound and defensible data. Let our team of professionals serve you today!
When a discharge permit is issued stipulating Whole Effluent Toxicity, testing must be initiated using both the fathead minnow (Pimephales promelas) and water flea (Ceriodaphnia dubia or Daphnia magna). Monthly testing is required during the first year of monitoring, however the permit holder may request a decrease in testing frequency to only the species identified as the more sensitive species. After completion of the first year of Whole Effluent Toxicity, and assuming previous Whole Effluent Toxicity studies have satisfactorily met permit requirements, the permit holder may again request a reduction in testing frequency to once per quarter. Upon renewal of a discharge permit, the permit holder is required to test both species to re-establish which organism is the more sensitive. In permit renewal situations the frequency of Whole Effluent Toxicity does not generally change. As with any changes to sampling frequency or requirements, confirmation of reduced monitoring eligibility should be confirmed with the regulatory agency overseeing regulatory compliance before changes are instituted.
The acute Whole Effluent Toxicity toxicity test endpoint is known as LC50 or lethal concentration 50. This point is achieved at the concentration level where 50% of the test species die within the testing period. The chronic test endpoint is known as IC25, or inhibition concentration. IC25 is the effluent concentration level where 25% of the test species demonstrate diminished growth or reproduction.
Toxicity units are the measurement units for effluent toxicity and are also the measurement units expressed in Whole Effluent Toxicity regulatory permits. TUa (toxicity unit acute) is determined by dividing the LC50 concentration into 100. TUc (toxicity unit chronic) is determined by dividing the IC25 concentration level into 100.
Permit requiring TUa 2.0 at a concentration of 50%;
LC50 = 60% effluent concentration
100÷60 = 1.67 TUa
This test result successfully passes permit specifications.
Permit requiring TUc 1.0 at a concentration of 100%;
IC25 = 75% effluent concentration
100 ÷ 75 = 1.33 TUc
This test result does not successfully pass permit specifications.
A test failure occurs when the test has a toxicity unit higher than the permit limits. If a failure occurs, a follow up test is performed in accordance with permit specifications to determine if the toxicity units remain above the permit limits. If the TU remains above permit levels, accelerated testing and / or a toxicity reduction evaluation (TRE) may be necessary. Accelerated testing requires the permit holder to perform Whole Effluent Toxicity tests on a more frequent basis. A toxicity reduction evaluation (TRE) is an in-depth site-specific plan designed to identify the cause of the effluent toxicity and the necessary actions to eliminate the toxicity. Increased Whole Effluent Toxicity testing is also necessary during a TRE.
Whole Effluent Toxicity provides an important safeguard in the balance between man and a healthy, thriving environment. Our goal at McCoy & McCoy Laboratories, Inc. (MMLI) is to assist clients in all phases of Whole Effluent Toxicity testing, including initial testing, reduced monitoring status, repermit screening, toxicity identification evaluations (TIE) and toxicity reduction evaluations (TRE). MMLI employs a highly trained and knowledgeable Whole Effluent Toxicity staff experienced in all phases of Whole Effluent Toxicity compliance. The staff participates in continuing education programs hosted by state, federal, and professional organizations to keep current on procedural and regulatory changes in the field. An in-depth quality assurance program is in place which includes federal EPA and state regulatory agency audits, an aggressive in-house QA / QC program and participation in third party QA / QC studies.