Bioassay PEEP index

Based on the correlation matrix of all bioassays data obtained with 37 effluents, it can be concluded that none of the bioassays produces data that are redundant. In other words, all bioassay procedures add to the information content of the PEEP index. 

Originally, the PEEP index was designed to assess industrial and municipal effluent toxicity (Section 3). Because the PEEP index formula can accommodate any number and types of bioassays, it could also be applied in other versatile ways (Section 8). 

PEEP index Potential Ecotoxic Effects Probe index Bioassays employed in effluent studies... 

As seen further on in this chapter, individual PEEP index values express a condensed portrait of an effluent s hazard potential which takes into account several important ecotoxicological notions (toxic intensity and scope in terms of biotic levels impacted, bioavailability, persistence of toxicity and effluent flow). Unlike wastewater investigations limited to chemical characterization, this bioassay-based scale reflects the integrated responses of several representative toxicity tests to all interaction phenomena (antagonistic, additive and/or synergistic effects) that can be present in effluent samples. 

At the time of its conception, the PEEP index integrated the results of a selection of practical small-scale screening bioassays which included the Vibrio fischeri bioluminescence inhibition test, the Selenastrum capricornutum growth inhibition... 

In the Toyama Bay Japanese effluent study, 20% endpoint effect values (e.g., LC20s for the D. magna assay and IC20s for the S. capricomutum assay), which are close approximations of TC values determined from NOEC and LOEC data (as in the Canadian study), were transformed into TU values and integrated into the PEEP formula. In applying the PEEP index concept to a designated series of wastewaters discharging to a common aquatic environment, it is paramount, of course, to use the same battery of bioassays and to report all of their toxicity responses with the same measurement endpoint and statistical analysis system (i.e., TC values for all effluents... 

Once toxic units are calculated for all bioassays, they are integrated in the toxic print portion of the PEEP formula, which is multiplied by effluent flow datum (Q = 3213 m3/h). The product of toxic print and flow yields the toxic loading of the effluent. The resulting PEEP index value of 5.8 is then simply the log10 of the calculated effluent sample toxic loading (plus 1). The value of 1 , inserted into the PEEP formula just ahead of the toxic print, insures that the inferior scale of the PEEP index will commence at 0 for effluents which are non toxic (i.e., those where toxicity responses are absent for all of the bioassays and which yield a ETz value = 0). 

Requiring low-sample volume micro-scale tests for its cost-effective application, the PEEP index has thus far employed bioassays with bacteria, algae and microinvertebrates. While well-standardized toxicity tests using freshwater fish existed at the time of the PEEP s conception in the early 1990 s (e.g., the Environment Canada fingerling rainbow trout 96-h lethality test to assess industrial wastewaters), they were excluded because of their large sample volume needs (e.g., close to 400 L of effluent sample required to undertake a multiple dilution 96-h LC50 bioassay in the case of the trout test). In addition to effluent sample volume, the cost of carrying out salmonid fish acute lethality bioassays for the 50 priority industrial effluents identified under SLAP I (the first 1988-93 Saint-Lawrence River Action Plan) was prohibitive. 

PEEP index mapping of major waterways and their associated tributaries (employing highly sensitive bioassays) to identify environmental hot spots and pollution sources. 

Measurement endpoints result in a waste PEEP index value (similar to the PEEP index presented in the Chapter 1 of this volume) resulting from the integration of different bioassay responses. ... 

The waste PEEP index formula can be employed with any appropriate number and type of tests depending on laboratory expertise and means (any bioassay can be replaced by another or added to the proposed list). In theory, waste PEEP index values can vary from 0 to infinity. In practice, it has been shown to produce values ranging from 0 to 10, thereby simulating a readily-understandable "waste scale" indicative of ecotoxic impact. 

To facilitate the integration of measurement endpoints from different bioassays into a single hazard index value, data need to be expressed on the same scale of measurement. Therefore, prior to calculating each effluent PEEP index value, the measurement endpoint of each bioassay is converted to toxic units (TU), by means of the following equation ... 

Where n is the number of bioassays exhibiting calculable (geno)toxicity responses, N is the total number of bioassays carried out, Ti is (geno)toxicity expressed in TU of each test. In quantifying the toxicity of leachates produced in the prerequisite study or in the WASTOXHAS procedure, the waste PEEP index allows clear identification of the most problematic wastes requiring priority in terms of clean-up action or attention. 

The following four bioassays are used to derive the PEEP index ... 

To apply the PEEP index, the effluent sample is first evaluated using all four bioassays. After biodegradation, the sample is tested using three of the four toxicity tests the Ceriodaphnia test is excluded. 

Results of all bioassays are reported as TOEC values, so a value can be entered into the PEEP index even if no inhibitory concentration (IC) or median effective concentration (EC50) was determined. The TOECs are converted to toxic units. The PEEP is calculated as the sum of the toxic units, including both before and after biodegradation, according to the following formula ... 

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