Study on the Effect of Residual Chlorine on the Viability of Marine Organisms
Environmental Research Section
At Tomatoh-Atsuma Thermal Power Station, we have started to the inject sodium hypochlorite (NaClO) into the water intake channel in order to inhibit biofouling followed by some obstacles to power generation or increase of biofouling waste. To start injection of NaClO, we had to pay the closest attention to the concentration of residual chlorine in the seawater so that we wouldn't cause damage to marine organisms but could inhibit biofouling. However, the information about the effect of residual chlorine on fish and shellfish living in north of Japan was not sufficient. Especially there was little precedent that had investigated the viability of eggs and larval fishes against residual chlorine.Therefore, we have carried out the exposure test to NaClO using fertilized eggs of brown sole (Pleuronectes herzensteini) that was an important fish for the fishery around Tomakomai coastal sea area, in order to confirm the effect of residual chlorine at low concentration on it.
Materials and methods
The material and method of the exposure test was as follows:
- Matured fishes of brown sole caught in coastal area of Hokkaido were allowed to spawn naturally and eggs were fertilized in a spawning tank.
- Six developmental stages (from fertilization to hatching) were investigated.
- Eggs were exposed for 15 minutes to the seawater set the concentration of residual chlorine at five levels (0.0, 0.2, 0.5, 1.0, 2.0 mg/L) and the temperature at two levels (10
: simulated temp. of intake water at a spawning season, 17: simulated temp. of outlet water). - Hatching rate of the eggs were counted.
Photo-1 Fertilized egg
(0 days after fertilization)
Photo-2 Larval fish
(4 to 5 days after fertilization)
Fig. 1 Changes of hatching rate by residual chlorine concentrations
Results
According to the following results, we have confirmed that the injection of NaClO into the water intake channel has had no effect on the hatching of the eggs of brown sole.
- There was no effect of residual chlorine on the hatching at 0.5mg/L as expected maximum concentration set by the NaClO injector on power station.
- There was no effect of the temperature at two levels on the hatching.
Plan for the Future
We plan to monitor the ecosystem around the sea area of Tomatoh-Atsuma Power Station before and after the start of NaClO injection. And we would like to contribute to reduce the environmental load caused by our power station through further research and development.
