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平成17年度 船舶バラスト水等処理技術実用化のための調査研究 報告書

 事業名 船舶バラスト水等処理技術実用化のための調査研究
 団体名 日本海難防止協会 注目度注目度5


7 EVALUATION BASED ON PBT CRITERIA
 Both the Ozone (Active Substance) and bromate ion (relevant chemical) have naturally acute toxicity. The half-life period of Ozone in the water is 5.8 seconds in the seawater and about 30 minutes in the fresh water, while that of bromate ion is about 12 hours apparently shorter than 60 days. The absorption coefficient, Koc, is as low as 27x10-8L/kg and cannot be categorized as the persistent. Bioaccumulation for bromate ion with comparatively low decomposition rate is as low as -7.18 in logPow. Therefore, both the Ozone and bromic acid do not fall under the category of PBT substances.
 
Table 9. Risk characterization
Substance Persistent (y/n) Bioaccumulative (y/n) Toxic (y/n) Reference/comments
Ozone no No Yes See Sections 3 and 6.
Bromate ion no No Yes See Sections 3 and 6.
 
8 TOXICITY TESTING OF THE TREATED BALLAST WATER
 As described in "paragraph 6.1.2, Chronic toxicity", there is no data on the chronic toxicity of Ozone and bromate ion. This ballast water treatment system dissolves the Ozone gas with the special structure of the disinfection unit and disinfect the aquatic organisms by the acute toxicity of Ozone and bromate ion (a relevant chemical) (see section 1, Introduction). It is considered that there is no potential of chronic toxicity of discharged ballast water since the Ozone as decomposed in an extremely short time to the level of 0.14μg/L which is the concentration of Ozone where it may exist in the environmental water. It is also considered that bromate ion which is a relevant chemical generated by the reaction of Ozone with the seawater has little impact because its acute toxicity is even under 0.16 mg/L, 1/200 of NOEC in addition to compliance with NOEC: 32 mg/L due to the tank holding time and the functions of the discharge treatment unit at the time of discharge. However, since there is no data on the chronic toxicity of bromate ion, it was determined as a prudent policy to prepare a sample of the discharged ballast water in accordance with the actual ballast water treatment and carry out a chronic toxicity test of the discharged water for evaluation.
 
 This system can be enhanced to be installed on board if the flow rate at the slip plates of the sterilizing treatment unit as well as the Ozone gas feeding concentration are kept constant and its scale can be further upgraded to comply with the land testing requirements provided in the Guidelines (G8) by increasing the diameter of the passage of the special pipe and the volume of Ozone gas to be supplied. From the result of toxicity in the test described below, toxicity in the operation on an actual ship and for the final approval in accordance with the Procedure (G9) will be able to be predicted in advance.
 
8.1 Test method
 
 The test method is described in details in the unofficial report. The test was carried out by a method that allowed to evaluate the chronic toxicity of 3 organisms as follows:
 
.1 Growth prevention test on algae (Skeletonema costatum) by ozone-treated seawater;
 
.2 Chronic toxicity test of Ozone-treated seawater with crustacean (Hyale barbicorins); and
 
.3 Ozone-treated seawater toxicity test at initial stage of biology of fish (Oryzias javanicus)..
 
 To secure the reproducibility of test results and reliability of test reports, each step of test operations and the final report were based on the OECD GLP standard, “OECD Principles of Good Laboratory Practice” (1997, ENV/MC/CHEM(98)17)29.
 
8.2 Test result
 
 The original test water was treated at the Ozone concentration of 4mg/L and stored at a dark place at about 4℃ and 25℃ each for 24 hours. Aquatic organism was exposed to the test water diluted to more than 1/10 of the original test water. The estimated bromate ion concentration (as the oxidant concentration) in the sample water is 0.16 mg/L or less.
 
 In the experiments, obvious chronic toxicity was not observed in the 3 types of aquatic organisms in the bromate ion concentration wider 0.16 mg/L. Therefore, the chronic toxicity NOEC of bromate ion generated by this system is estimated to be more than 0.16 mg/L. This value is a result with test water of TOC about 1.1 mg/L. This TOC concentration values are low in the normal fresh water and sea water. It implies, therefore, that these results were obtained in such an environment where the bromate ion is hard to be consumed or decomposed by organic substances, that is, an environment where strong toxicity is easily represented.
 
9 RISK ASSESSMENT REGARDING ENVIRONMENT
 It is evaluated that there is no risk of Ozone as an Active Substance related with the environment both in the fresh water and seawater since Ozone is decomposed in an extremely short time and not discharged outside the ship. Therefore, the risk evaluation to the environment hereinafter is focused on bromate ion which is a relevant chemical generated when the seawater is treated.
 
9.1 Short-term aquatic toxicity
 
 Acute toxicity of bromate ion in the seawater was the NOEC: 32 mg/L (oxidant analysis value as sodium bromate) to Crassostrea gigas in the existing data (see paragraph 6.1, Acute toxicity).
 
 On the other hand, the bromate ion concentration (as oxidant concentration) at the time of discharge from the special type hybrid system is less than 0.16 mg/L in many cases (tank holding time = more than 48 navigation hours).
 
 Therefore, it is considered that the short-term toxicity of ballast water discharged after being treated m this system is basically insignificant. Even when the tank holding time, in case navigation time is less than 48 hours, it can be evaluated to be safe enough due to the concentration lower than the acute toxicity NOEC and the effect of dilution with the surrounding sea water.
 
9.2 Long-term aquatic toxicity
 
 Since concentration of bromate ion (oxidant concentration) at time of discharge is lower than 0.16mg/L, there exists little anxiety of long term effects.
 
 However, a prediction computation by using model of MAM-PEC Version 1.630 was performed to ensure the above. Rotterdam Port in the Netherlands was hypothetically selected.
 
 Calculated concentration of bromate ion contains the following 4 cases: (1) 0.16mg/L concentration designed for this system at time of ballast water discharge, (2) 1.6 mg/L without decomposition treatment at the discharge treatment unit, (3) 3.44mg/L, average concentration by production after Ozone injection (prior to storage in the ballast water tank) and (4) 4.56mg/L. the maximum concentration after Ozone injection (prior to storage in the ballast water tank).
 
 This prediction computation showed that average concentration covering the whole part area would be 0.000722mg/L, compounded with the effect of dilution, if 0.16mg/L designed concentration of discharged bromate ion for Special Pipe hybrid system is applied. This predicted concentration is equivalent to 1/575 of 0.16mg/L concentration where no chronic toxicity arises. Average concentration for 1.6mg/L without decomposition treatment at the discharge treatment unit is predicted as 1/57 of 0.16mg/L 10 years later. Safety related to long term effect will be sufficiently secured without decomposition treatment at the discharge treatment unit.
 
 Therefore, bromate ion to be discharged from this system will not cases any effects on aquatic organisms from stand point of long term and short term view.
 
10 EFFECTS ON HUMAN HEALTH
 A scenario of influence on men (excluding the crew) through the marine organisms (ecosystem) is potentially considered. However, since there is no effect on the environment, concentration in marine organisms will not be caused. Thus, there is no risk of effects.
 
11 EFFECTS ON SAFETY OF LABOUR (CREW)
 For this system, leaking Ozone densitometers are provided around the Ozone generator and close to the transfer route to monitor the leaking Ozone continuously. If leaking Ozone is detected, visible and audible alarms are raised at the bridge and the location of the system to stop operation of the generator and urge the crew to evacuate. Therefore, there is no possibility of exposure to the crew in the normal operation of the Ozone, an Active Substance of this system.
 
 Possibilities of exposure to the crew due to discharge of Ozone gas caused by casualties, should be examined in advance. Generally assumed casualties onboard are confined to fire and flooding. If a fire breaks out in the engine room, this system in the engine room can be stopped emergently from the outside of the engine room like the fuel pump and can stop the generation of Ozone which may grow the fire. If the engine room is flooded and this system is soaked in water during operation, there is no possibility of secondary accidents. Only electrical parts are short-circuited and stop. Details are described in the unofficial version.
 
12 EFFECTS ON HULL
 When this system is installed on board a ship, effects of Ozone causing corrosion should be first considered among effects on the bull. As Ozone has strong oxidizing property, materials should be selected taking consideration to the corrosion resistance.
 
 In accordance with the result of electrochemical analysis and corrosion tests by using the designed Ozone concentration of this system, the area required for selection of the materials were identified.
 
 If the Ozone concentration (oxidant concentration) in the seawater is 0.3 mg/L. which is a value immediately after the designed treatment (immediately after Ozone is supplied to the disinfection treatment unit), corrosive influence on bare steel plates or galvanized steel plates is not so different from that in the seawater containing no Ozone and the corrosive influence of Ozone can be ignored.
 
 Since the Ozone dissolution speed is high, the concentration decreases to under 0.3 mg/L within the piping to the deaerating tank. Therefore, no corrosion measures are required in the piping after the deaerating tank and in the ballast tank. However, the piping from the Ozone inlet to the pump and the deaerating tank is continuously exposed to Ozone. Therefore these parts should be made of Ozone resistant materials such as stainless steel for the safety.
 
 Corrosion-proofing effect can be maintained with epoxy coating for several hours but this effect decreases rapidly when exposed longer continuously. Therefore, use of epoxy coating should be avoided in piping exposed to Ozone continuously for a long time.
 
 As described above, in a ship where this system is installed, materials of equipment or piping are selected considering the corrosive influence of Ozone and therefore the hull is not subjected to such influence of Ozone. In this context, oxidizing property of bromate ion is weak and can be avoided by the measures against the corrosive effects of Ozone.
 
 The range in this system requiring the corrosion measures of Ozone is only the area provided additionally for installing this system. It was found out that the piping after the deaerating tank and the ballast tank can be handled in the same manner as with the traditional seawater ballast.


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更新日: 2019年9月21日

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