PEEP index/scale

Table 11. PEEP index scale for the hazard assessment of wastewater samples using a reduced test battery.

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. 

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. 

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... 

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... 

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). 

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. 

Hazard potential for each effluent was calculated using a mathematical formula (the PEEP index) proposed by Costan et al. (1993). This formula integrates the ecotoxic responses of the battery of tests before and after a biodegradation step. Toxicity test endpoint responses are first transformed to toxic units. The product of effluent toxicity and effluent flow (m3/h) gives the toxic loading value. The log 10 value of an effluent s toxic loading corresponds to its PEEP index. In order to rank the effluents a toxicity classification scale is generated (Tab. 11). 

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 ... 

Table 8. Field scale study - Ecotoxicity of accumulated percolates of a municipal solid waste incinerator bottom ash (BA) and a slag from a second smelting of lead (2SL) from field experiments and their corresponding waste PEEP index values (see Section 5.6 for the detail of calculations).

Environment Canada recently developed an evaluation system based on effluent toxicity testing, capable of ranking the environmental hazards of industrial effluents [185]. This so-called Potential Ecotoxic Effects Probe (PEEP) incorporates the results of a variety of small-scale toxicity tests into one relative toxicity index to prioritize effluents for sanitation. In the index no allowance has been made for in-stream dilution, therefore the acmal risk for environmental effects is not modeled. The tests performed on each effluent are the following bacterial assay [V.fisheri (P. phosphoreum), Microtox], microalgal assay S. capricornutum) crustacean assay (C. dubiay, and bacterial genotoxicity test E. coli, SOS-test). 

Blaise, C. and J.F. Ferard. 2005. Effluent assessment with the PEEP (potential ecotoxic effects probe) index. In C. Blaise and J.F. Ferard. (eds), Small-scale Freshwater Toxicity Investigations, Vol. 2, pp. 69-87. New York Springer. 

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