December 16, 2004
The Ministry of the Environment announced the results of groundwater quality monitoring conducted by the national and local governments in FY 2003 pursuant to the Water Pollution Control Law. The Law provides that the governor of a prefecture shall monitor the quality of groundwater in accordance with the groundwater quality monitoring program prepared annually by each prefecture.
1. Results of general monitoring survey
The overall condition of groundwater pollution is evaluated based on the result of the general monitoring survey which aims to hold the overall condition of the local groundwater. In FY 2003, the survey was conducted on 5,129 wells in 1,716 municipalities.
Table 1 shows the monitoring results. Among the 5,129 wells surveyed, 421 wells have some items exceeding the environmental quality standards (EQSs). The proportion of wells exceeding the EQSs is 8.2% (6.7% in FY 2002). Among the substances most commonly found to exceed the EQSs, nitrate nitrogen and nitrite nitrogen have the highest ratio, 6.5% (5.9% in FY 2002).
The results of the questionnaire conducted by the Ministry of the Environment about the groundwater pollution also indicate that the number of cases exceeding the EQSs for nitrate nitrogen and nitrite nitrogen tend to increase every year. (Reference)
Arsenic and fluorine can sometimes be detected in groundwater due to natural causes. EQS exceeding rate of these two are leveling off. For other 15 substances including cadmium, no wells are found exceeding the EQSs
Table 2 shows the changes in the EQS exceeding rate in general monitoring surveys conducted after establishment of the EQSs.
|2.||Pollution of groundwater by nitrate nitrogen and nitrite nitrogen|
It is known that intake of water containing more than a certain amount of nitrate nitrogen and nitrite nitrogen causes a disease which loses the ability to carry oxygen in blood system ,resulting oxygen shortage in the body (methemoglobinemia). The victim of this disorder is usually babies and infants. Causes of groundwater pollution by nitrate nitrogen and nitrite nitrogen are fertilizer, household wastewater and livestock excreta. Most of the cases, range of pollution can be wide.
Table 3 shows the survey results of nitrate nitrogen and nitrite nitrogen by prefectures in the monitoring survey. It indicates that the EQS exceeding rate is high in Gunma, Ibaraki, Saitama, Chiba, and Tochigi prefectures in Japan.
The Ministry of the Environment has been preparing the manuals and compiling the case studies to promote effective measure for reducing the load of nitrogen according to the local cases, as the countermeasure for nitrate nitrogen and nitrite nitrogen. And it has also been conducting studies for the development of groundwater purification technology by non-point sources pollution which tends to be widely spread. The Ministry of the Environment is to promote overall countermeasure against the groundwater pollution by nitrate nitrogen and nitrite nitrogen based on the results of these surveys.
Nitrate nitrogen and nitrite nitrogen is designated as one of the monitoring items* in 1993, and added to the list of substances for which EQSs are set in 1999. Since then, state of water pollution by these two items has been monitored. Compared to the other items, their EQS exceeding rate has been higher.
|*||The monitoring items are substances that may affect human health, but water quality survey results of public waters do not indicate a need for immediate establishment of the environmental quality standards (health item). It is recognized, however, that further accumulation of information on the substance is required.|
Fig.1 shows the changes in theEQS exceeding rate regarding top five items. (i.e., nitrate nitrogen and nitrite nitrogen, arsenic, fluorine, tetrachloroethylene, and trichloroethylene). Although tetrachloroethylene and trichloroethylene, which main pollution sources are factories, showed a downward trend since the introduction of underground infiltration prohibition in FY 1988, their ratio is leveling off in several years. For worse, new contamination is still detected. Arsenic and fluorine can sometimes be detected in groundwater due to natural causes such as elution from rocks and soil.
When a well supplying drinking water is found to be polluted, the local government provides guidance to well users not to drink well water in order to prevent health damages.
|* Reference||Results of the Questionnaire about Groundwater Pollution Cases in FY 2003|