4.3 Present Condition of Pollution by Hazardous Chemicals (Dioxins)

　　Almost all the dioxins contained in the contaminated water exist in the particulate mater in the water because the solubility of dioxins is extremely small in general.

　　Environment Agency of Japan monitored the concentration of dioxins in rivers and lakes in 1986 as a monitoring plan for contamination of hazardous chemicals. Only 1,3,6,8-TCDD (detected in 9 samples among 18 samples) and Octa-CDD (detected in 4 samples among 18 samples) are detected.

　　Environment Agency of Japan surveyed the concentration of dioxins in sea regions such as Tokyo Bay, Ise Bay, the Seto Inland Sea and so on in March, 1996, and disclosed the result as shown in Table 4-2 in May, 1996.

　　The concentration levels are 0.0000 - 0.0003 ng TEQ/L, where TEQ is "toxicity equivalent quantity". In the isomer pattern, O₈CDD is detected in all the samples and then 1,2,3,7,8-P₅CDF is detected in the 58 % of all the samples. The detected ratio of the other isomers is 0 - 17 % in the all samples.

Table 4-2 Average Concentration of Dioxins in Seas (fiscal year of 1995)

Note: N.D. means "not detectable". Detected limit is 0.001 ng/L