User Guide to Thresholds and Classification - Environmental ...

413User Guide for Thresholds and ClassificationsNote: LC 50 = median lethal concentration; LD 50 = median lethal dose; ppm = parts per million.Mixtures with highly ecotoxic components (multiplication factors)The steps to follow in applying the summation approach to terrestrial hazard classification for mixtures withhighly ecotoxic components are set out below Table 21.5.Table 21.5: Example of the summation approach for a mixture containing highly toxic componentsComponentLD 50(mg/kg bw)Individualsubstance(100%)classificationConcentration in mixture(%)MultiplyingfactorB 55 9.3B 5 - 5P 0.2 9.3A 0.05 100 5Q 9 9.3A 1 - 1T 1,000 9.3C 40 - 40U Not classified Not classified 53.95 - 53.95Weightedconcentrationof individualsubstance inmixture (%)Note: bw = bodyweight; LD 50 = median lethal dose.Step 1Component P is highly ecotoxic and attracts a multiplier of 100, resulting in a weighted concentration ofthat component of 5%.Component Q, although classified as 9.3A is not given addition weighting, that is:(100 x P) + Q(100 x 0.05%) + 1% = 6% , which is < 25%so the mixture Z is not classified as 9.3A.Step 2: Consider components classified as 9.3A and 9.3B.10((100 x P) + Q) +B10((100 x 0.05%) +1%) + 5% = 60% + 5% = 65%, which is ≥ 25%so the mixture is classified as 9.3BJanuary 2012 EPA0109