PEEP index

All test results are expressed as threshold values (LOECs), and subsequently transformed to toxic units (TUs). The entire scheme results in a total number of 10 TUs per effluent. The results are put through the following calculation to produce the 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). 

Table 1. Summary of the PEEP index hazard assessment scheme for effluents.

PEEP index Potential Ecotoxic Effects Probe index Purpose... 

In theory, the PEEP index can vary from 0 to infinity. In practice, it has been shown to produce values ranging from 0 to about 10, thereby simulating a readily-understandable "environmetal Richter scale" indicative of point source industrial toxicity. 

Because of the mathematical formula employed, the PEEP index can be... 

Historical overview and applications reported with the PEEP index... 

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. 

Advantages of the PEEP index scheme for effluent assessment... 

Outstanding PEEP index characteristics can be summarized as follows ... 

The PEEP index formula, is easy to use and interpret, and capable of accommodating any number and types of toxicity tests, thereby enabling its application internationally. 

Application of the PEEP index provides unambiguous capacity to discriminate between effluents having low and high toxic loading potentials. 

Numerical PEEP index values are the log10 expression of an effluent s toxic loading (= toxic potential of effluent generated with a relevant battery of toxicity tests multiplied bv effluent flow) and normally vary between 0 and 10. The PEEP scale can thus be considered as a type of environmental Richter scale for... 

While the PEEP index can theoretically be employed to assess the toxic potential of varied liquid media and groups of specific chemical products of interest (Section 8.3), it was originally conceived to appraise that of liquid wastes of point source discharges to aquatic environments. The index is thus described for this purpose in this section. 

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... 

The formula enabling the determination of effluent PEEP index values with the description of its various components is shown in Fig. 2. It takes into account... 

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). 

Figure 3. PEEP index calculation for actual toxicity data obtained for a Pulp Paper effluent.

In applying the PEEP index concept to sets of industrial effluents thus far, wastewater samples have been filtered prior to bio-analysis (see Section 5.1). Hence, only their soluble toxicity potential is taken into consideration. This is certainly a drawback at this time as toxic and genotoxic potential linked to suspended matter of some industrial plant effluents, for example, have been shown to be important (White et ah, 1996 Pardos and Blaise, 1999). Particulate toxicity in effluent samples should certainly be addressed in future PEEP applications, as soon as reliable small-scale toxicity tests are developed and available to estimate it. Indeed, the issue of soluble and particulate toxicity is especially relevant in relation to technology-based reduction of hazardous liquid emissions. 

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. 

Table 2. Reproducibility of effluent PEEP index values.

Box 1. Other possible applications of the PEEP index concept. 

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