Leeches as in situ biomonitors of chlorinated phenolic compounds. Part 2: Pulp mill investigations

Leeches (Nephelopsis obscura Verrill) were evaluated as in situ biomonitors of chlorinated phenolic compounds in the Fraser River at Prince George, BC, downstream from three bleached kraft pulp mills practising chlorine dioxide (ClO2) substitution. Five biomonitoring periods, of 7 days duration, were selected to cover a full range of seasonal river conditions. Leeches bioconcentrated tri- and tetrachlorinated phenolics (bioconcentration factors: 465–6000) in proportions similar to those present in both mill effluent and river water. Leeches showed 3,4,5-trichloroguaiacol (3,4,5-TCG) to be the most consistent tracer of bleached kraft mill discharge. Leeches provided direct evidence that increasing ClO2 substitution reduces amounts of chlorinated phenolics accumulated by aquatic organisms, with sharp decreases observed at ClO2 levels greater than 90%. This study suggests that leeches could be applied as routine biomonitors for environmental impact monitoring.