This webinar series focuses on polychlorinated biphenyls (PCBs) in schools and features SRP grantees, as well as EPA and international partners. During this second session, Gabrielle Ludewig, a professor and SRP researcher at the University of Iowa, will give an overview of the mechanisms of toxicity; Geniece Lehmann, an EPA Toxicologist, will discuss evaluating the noncancer health risks from inhaled PCBs; and Niklas Johansson of the Swedish Environmental Protection Agency will give an international perspective on PCB inventory, remediation, and outcomes.
Professor, Department of Occupational and Environmental Health
Overview of Mechanisms of Toxicity
The number and placement of chlorine atoms on individual PCBs determine their physical properties (solubility/lipophilicity, vapor pressure, melting point, planarity, chirality) and their biologic/toxicologic characteristics (binding to receptors, induction, repression and inhibition of xenobiotic metabolism, resistance to metabolic attack, activation to electrophilic species, and propensity for secretion/excretion). Airborne PCBs are more volatile and more readily metabolically activated. For this latter group of lighter PCBs and their metabolites, sensitive toxic endpoints may include: genotoxic endpoints (point mutations, chromosome breaks and loss, sister chromatid exchanges, polyploidizations, telomere shortening) and interference with vitamin and hormone transport, especially thyroid hormone availability. Several of the above effects have been observed at nanomolar concentrations in vitro. The challenge for the toxicologist will be to identify those operative in vivo for those persons exposed to airborne PCBs at levels found in school environments.
Toxicologist, U.S. EPA
Evaluating Noncancer Health Risks from Inhaled PCBs
In some buildings, indoor air PCB concentrations can be up to one or more orders of magnitude higher than ambient outdoor concentrations. In some indoor settings and for some age groups, inhalation may contribute more to total PCB exposure than any other route of exposure. In recognition of this particular route of exposure, efforts have been made to assess the potential health risk posed by inhaled PCBs. PCB exposure has been associated with human health effects, but data specific to the inhalation route are insufficient to support exposure response assessment. For this purpose, it is critical that future investigations of the health impacts of PCB inhalation carefully consider certain aspects of study design, including characterization of the PCB mixture present. This presentation will describe critical areas of research needed to reduce some of the uncertainty in evaluating risks for inhaled PCBs. The views expressed in this presentation are those of the author and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.
Swedish Environmental Protection Agency
International Experience: Inventory, Remediation, and Outcomes
During the 1950s up to the late 1970s, or in some countries even later, PCBs were used in considerable amounts in buildings and other construction mainly as plasticizer and stabilizer in caulk, flooring materials, paint and glue. There are only rough estimates of the total amounts that were used in buildings and construction and even more uncertain information on remaining amounts. It has been shown that PCBs in these open applications are continuously volatilizing into both outdoor and indoor air and that the elevated levels in indoor air can cause elevated concentrations in the blood of inhabitants in such buildings. Based on the information that PCB can cause negative health effects in both man and environment, many countries in the 1970s introduced legal restrictions on the production and use of PCBs. Many countries have launched specific programs in order to remove PCBs also in open applications. Sweden has issued an "Order of PCBs etc." containing specific legislation on nation-wide identification, removal and destruction of PCBs in open applications as buildings and construction. International actions in order to reduce human and environmental exposure to PCBs have also been taken. The most important international agreements are the Stockholm Convention on POPs and the Convention on Long-range Transboundary Air Pollution (CLRTAP) that includes a Protocol on Persistent Organic Pollutants (POPs). Experiences from these national and international activities will be summarized and a some important recommendations will be discussed.