Identifying Iron Foundries as a New Source of Unintentional Polychlorinated Naphthalenes and Characterizing Their Emission Profiles

摘要

Iron foundries have been identified as dioxin sources in previous field investigations. Similar formation mechanisms between dioxins and unintentional polychlorinated naphthalenes (PCNs) have led us to speculate that iron foundries are also potential PCN sources. In this study, PCNs in stack gas and fly ash samples representing atmospheric and residue emissions from 13 typical iron foundry plants were analyzed. The average emission factor of ∑_(2-8)PCNs to residue was calculated to be 61 μg t~(-1), with a range of 10-107 μg t~(-1). The emission factors of ∑_(2-8)PCNs to air in two case plants were 267 and 1472 μg t~(-1). The derived emission factors might be useful for estimating annual emissions and understanding the contribution of PCNs from iron foundries. The possible formation mechanisms of PCNs, based on the PCN profiles, are discussed. Successive reductions in the abundance of homologues were observed to occur with the increase in chlorine substituted numbers. Abundances of congeners containing more β-position chlorines in the naphthalene skeleton were much higher than those of congeners containing more α-position chlorines for penta-, hexa-, and hepta- homologues, which suggests that the β-positions are favored for chlorination. Potential chlorination pathways from tetra- to octa- homologues are proposed.