State of water environmental issues
2. Water Quality Monitoring Items, etc.
(1) Monitoring Items
EQS items (Reference 1) are mainly classified into two types: items relating to human health protection (hereinafter referred to as ”human health items”), such as cadmium and total cyanide; and items relating to living environment preservation (hereinafter referred to as ”living environment items”), such as BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand), and pH (hydrogen ion concentration).
Human health items comprised eight of these items in 1971 when the first water quality survey started. However, as a result of the sequential addition of new items since then, the total number of human health items has now risen to 26. In some cases, substances relating to human health protection may be temporarily classified as a “Monitoring Substance” instead of an EQS item if, after full consideration of the results of their detection in public water areas, it is determined that there is still a need to continuously accumulate more data. When monitoring such substances, each prefectural government strives to collect relevant knowledge by positioning those substances as key issues in their water quality monitoring plans. In 1993, 22 items were classified as monitoring substances and five more items were added to the list of monitoring substances in 2004. The total number of monitoring substances has now risen to 27.
In general, EQSs for human health items are applied to all public water areas. However, both fluorine and boron EQS values should not be applied to seawater areas because their natural concentration in the sea exceeds the specified EQS values.
The list of living environment items initially comprised only seven items in 1971, but total nitrogen and total phosphorus were added to the list in 1982 and, in 2003, total zinc was also added in consideration of the need to conserve aquatic life. Thus, the total number of living environment items has now risen to 10, with total zinc and three other items being selected as monitoring substances relating to aquatic life.
EQSs for living environment items should only be applied to water bodies for which an EQS type has been specified by the national or prefectural government, based on the water usage by each water body group, such as rivers, lakes and reservoirs, and seawater areas (hereinafter referred to as “Specified Water Bodies by Type”). Therefore, the results of water quality surveys carried out on these specified water bodies by type have also been included in this report.
Monitoring of THM-FP, which is classified as a specific item under the provisions of the “Law Concerning Drinking Water Sources”, started in 1995.
(2) Number of Monitoring Points and Number of Samples
Table 1 shows the number of specified water bodies by type, the number of monitoring points used, and the number of samples collected in 2006. For human health items, the number of monitoring points decreased by 2.0%, compared to the previous year, while the number of samples decreased by 8.4%. For living environment items, the number of monitoring points and the number of samples decreased by 0.7% and 2.7%, respectively. The survey for total zinc was conducted at 4,825 points, using 26,130 samples.