US EPA

199182 

Technical Report 

Sources of and human exposure to PCDDs and PCDFs 

Rappe, C 

1991 

Cold Spring Harbor Laboratory Press 

Cold Spring Harbor, NY 

121-129 

Polychlorinated dioxins and poly chlorinated dibenzofurans (PCDDs and PCDFs) can be produced by a variety of primary sources. Human exposure occurs primarily via secondary or semisecondary sources such as ingestion of food and drinking water and through dermal contact and inhalation. The primary sources of PCDDs and PCDFs include chemical reactions and thermal and photochemical source. Analyses of archived samples of soil and vegetation show that low levels of PCDDs and PCDFs can be identified in 150-year-old samples; however, these levels have been shown to increase between 1940 and 1986. Mass balance estimates indicate a pronounced difference between the known emissions of PCDDs and aerial deposition, the latter being approximately 10-20 times higher.