Effects of pulp mill effluent on goldfish in the Waikato River - before and after changes to the bleach plant process

Abstract

The Kinleith pulp and paper mill discharges biologically treated bleached kraft mill effluent into the Kopakorahi arm of Lake Maraetai (New Zealand). The discharge of effluent from the Kinleith mill results in an effluent gradient defined by relatively low visibility (Secchi disc), transmittance ( 465 run), and dissolved oxygen levels and relatively high water temperatures. The composition of fauna caught in fyke nets reflects this effluent gradient and at the most effluent-exposed sites is dominated by the goldfish and is depauperate in pollution-sensitive species such as freshwater crayfish and trout. In June 1991 the pre-bleaching and bleaching processes at the Kinleith mill were extensively modernised. A two-stage oxygen deligni:fication system was introduced and the bleaching sequence converted to an elemental chlorine free process using 100% chlorine dioxide substitution. These changes were expected to have a substantial impact on the characteristics of the effluent discharge. Following the 1991 process modifications there have been improvements in the Secchi disc visibility, transmittance, temperature and dissolved oxygen levels at effluent-exposed sites. Improvements in the water quality of the receiving waters are reflected in changes in the sampled fauna. The sublethal effects of effluent from the Kinleith mill on the goldfish, Carassius auratus, living in the Waikato river were examined both before and after the modernisation of the bleaching process. Sublethal effects were seen in the haematological response, condition indices, and the histopathology of the liver, biliary tract, pancreas, kidney, gonads, and fins of goldfish from sites receiving effluent from the Kinleith mill. Several parameters in the goldfish were shown to be biomarkers sensitive to exposure to effluent from the Kinleith mill including: elevation of abnormal red blood cells; increased numbers of melano-macrophage centres and changes in their histochemistry; proliferative and neoplastic responses of the liver, biliary tree, and pancreas; hyperplasia of the pancreatic islets; the prevalence of immature nephrons in the kidney; necrosis of vitellogenic ova associated with chronic inflammation of the surrounding ovarian tissue in female goldfish; intersexuality; and the prevalence of fin erosion. Many of these parameters have not previously been identified as potential indicators of exposure to pulp mill effluent. Modernisation of the bleaching process at the Kinleith mill was reflected in improvements in some aspects of the haematological response and in a reduction of the prevalence of fin erosion. In conclusion. effluent from the Kinleith pulp and paper mill was shown to result in a variety of sublethal effects on the health of goldfish in the Waikato river despite the presence of secondary treatment of the effluent. Whilst improvements in some parameters were seen following process modifications in the bleach plant, recovery must be regarded as incomplete. Clearly, at least some mills with secondary effluent treatment of the effluent and modernised bleaching processes, including chlorine dioxide substitution. may continue to elicit sublethal effects in fishes from receiving waters.