Dioxin - Benchmarks, Standards and Guidelines Established to Protect Public Health

The following is a description of some the benchmarks, standards and guidelines EPA used to evaluate environmental conditions in the aftermath of the World Trade Center disaster.

Dioxin refers to a group of chemicals created when many types of materials burn; it is also created during some types of manufacturing and incineration. Dioxin does not break down easily, remains in the environment and can be distributed by wind and water. It is found in a wide variety of places. People are exposed to dioxin primarily by eating meat, dairy and fish.

The burning of building and office debris at the World Trade Center caused some emissions of dioxin. Most of the air samples taken in areas surrounding the work zone and analyzed for dioxin were below EPA's screening level, which is set to protect against significantly increased risks of cancer and other adverse health effects. The screening level is based on an assumption of continuous exposure for a year to an average concentration of 0.16 nanograms per cubic meter (ng/m3).* Because the vast majority of individual as well as the average** measured dioxin levels have been lower than the screening level, EPA does not expect an increased risk of health problems as a result of dioxin being emitted from the World Trade Center site.

* The unit, ng/m3, is the mass of dioxin/furan compounds in nanograms (a billionth of a gram) per cubic meter of air. Measurements of the dioxin/furan compounds are grouped together into a single value termed "dioxin toxic equivalents" or dioxin TEQs.

** For the purposes of evaluating exposure, an average concentration of many samples more closely represents exposure over a longer period. This longer term average is less than the maximum concentration that could be contacted at any one time, but because the screening level assumes continuous exposure for a year, the average of the measured concentrations is more appropriate for evaluating risk than an individual measurement.

See the Dioxin Fact Sheet

View Monitoring Data for Dioxin in Air