Physiological effects in fish exposed to effluents from mills with six different bleaching processes

Area of Science:

• Environmental toxicology
• Aquatic ecotoxicology
• Fish physiology

Background:

• Bleached kraft mill effluents (BKME) pose environmental risks to aquatic ecosystems.
• Understanding the toxicological effects of different BKME treatment processes is crucial for environmental protection.

Purpose of the Study:

• To assess the impact of various BKME treatment methods on rainbow trout (Salmo gairdneri R.).
• To evaluate hematological, osmoregulatory, and mixed function oxidase (MFO) responses in fish exposed to different BKME concentrations.

Main Methods:

• Continuous exposure of immature rainbow trout to six different BKME types at two concentrations for 7 weeks.
• Monitoring hematological, osmoregulatory, and MFO parameters post-exposure.
• Simulating Baltic littoral zone conditions using mesocosms.

Main Results:

• Conventional choline bleaching (C95 + D5)EHDED, with or without aerated lagoon treatment, caused the most significant adverse effects on fish.
• Oxygen prebleaching with high chlorine dioxide substitution (50%) or normal chlorine levels (85%) in the CD step resulted in the fewest negative impacts.
• Effluent composition influences MFO activity, suggesting a complex interplay of stimulating and inhibiting substances.

Conclusions:

• The treatment method for BKME significantly alters its toxicity to aquatic organisms.
• Oxygen prebleaching and chlorine dioxide substitution represent potentially less harmful BKME processing techniques.
• The biological effects of BKME on fish are complex and depend on the specific chemical composition of the effluent.