IDENTIFICATION OF SOURCES OF DIOXIN-LIKE PCBS IN SEDIMENTS OF JAPAN BY A CHEMICAL MASS BALANCE APPROACH Isamu Ogura*, Shigeki Masunaga**, Kikuo Yoshida* , ** and Junko Nakanishi* , ** *Research Center for Chemical Risk Management, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba 305-8569, JAPAN **Graduate School of Environment and Information Sciences, Yokohama National University, 79- 7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, JAPAN Introduction Dioxin-like PCBs (IUPAC Nos. 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189) are referred to as dioxin-related compounds and are evaluated together with PCDDs/PCDFs in terms of toxicity 1 . In Japan, the contribution of dioxin-like PCBs to the total TEQ of human intake is comparable to that of PCDDs/PCDFs 2 . Understanding the contributions from different PCB sources is important for developing effective countermeasures against dioxin pollution. The major sources of dioxin-like PCBs in Japan are considered to be those released from use or disposal of industrial PCB products and formed as byproducts during thermal processes 3, 4 . In this study, we estimated the contributions of these sources to the accumulation of dioxin-like PCBs in sediments using a chemical mass balance (CMB) approach and assuming that the dioxin-like PCBs in sediments mainly originated from Kanechlors (KCs: major Japanese PCB products) and incinerator emissions. Materials and Methods Chemical mass balance approach The chemical mass balance (CMB) approach has often been used to estimate the contributions of sources of target chemicals to an environment medium by comparing the compositions of chemicals in source emissions with that in the environment medium 5 . In this study, we estimate the contributions from different sources to the accumulation of PCB congeners in a sediment. The contributions of individual sources j (S j ) are calculated by minimizing χ 2 , as shown by χ 2 = 2 1 1 1 ∑ ∑ = =                 − k i p j j ij i i S a C C where C i is the mass concentration of congener i in the sediment, a ij is the mass fraction of congener i for source j, k is the number of congeners, and p is the number of sources (k>p). This approach is applicable under the following hypotheses. 1) Each source possesses a unique property (a ij ) that is not common to other sources. 2) Selected sources and their values of a ij are adequate. 3) The values of a ij of the emission from a source hardly change in the environment. In general, the input values of a ij have a certain extent of variability and uncertainty. Considering this, we also used the CMB approach with a Monte Carlo method by Crystal Ball Pro for Windows 4.0g (Decisioneering, Inc.). Organohalogen Compounds 56, 473-476, 2002