This paper describes the study conducted by People's Science Institute that aimed at determining the threshold level of toxicity of a paper mill effluent, and the level of toxicity that it created in the receiving water body and at identifying the  physico chemical parameters of the effluent that may be causing the observed toxicity. The study was conducted in Star Paper Mill in Saharanpur in Uttar Pradesh, which is one of the oldest and the largest paper mills in the country.

Evidence indicates that wastewaters generated from the processes in the paper mills contain a range of toxic chemicals such as mercury, chlorinated lignins and their derivatives, chlorides and suspended solids, which can be extremely harmful to living organisms in the water bodies. Many a times, the wastewaters are not recycled and are directly released as effluents into the water bodies.

A soda recovery plant within the Star Paper Mill in Saharanpur processes about 1700 m3/ day of black liquor from the pulping process. All wastewater from the mill is channeled through a single drain to the effluent treatment plant, where it is treated by activated sludge. The effluent is then released into the River Hindon, which is a seasonal river and has very low flows for much of the year.

Fish and Rice bioessays were performed to look at the impact of the effluents on the aquatic animals and plants. The study found that:

• Undiluted effluent from the Star Paper Mill, Saharanpur, exerted 100% mortality to fish of the species Barilius Bendelisis. In two of the fish bioassays (Tests 2 & 3), the toxicity of the effluent rapidly decreased with effluent concentration. The LC50 of the effluent samples for these tests were estimated at 90% effluent concentration. The threshold level of toxicity of the effluent occured at 70% effluent concentration.
• Results from one of the fish bioassays showed that toxicity decreased with effluent concentration at a lesser rate. The LC50 of the effluent sample for this test was estimated at 60% effluent concentration. The high toxicity observed in this test is likely due to the higher levels of mercury in the sample, when compared with samples taken for Tests 2 and 3.
• The fish bioassays indicated that after confluence with the Star Paper Mill effluent channel, water in the River Hindon would cause a mortality rate of 50 – 85% mortality on Barilius Bendelisis.
• Bioassay tests on rice seeds showed that the paper mill effluent was toxic to rice seed germination, but that the effects on the seedling growth after germination may be inhibitory or stimulatory, and vary with the growth stage of the seedling.
• The threshold level of toxicity with respect to rice seed germination was 25% effluent concentration. After confluence with the Star Paper Mill effluent channel, water in the River Hindon used for irrigating germinating rice seeds would cause a 50% reduction in seed percentage germination.
• The biochemical oxidation demand, chemical oxidation demand, and the concentrations of total suspended solids and mercury in effluents from the Star Paper Mill exceeded the maximum permissible limits.

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