Whenever I hear a number or statistic, I instinctively look for a comparison point. I also think about how that number impacts me personally. The soil dioxin study results we released last week probably raised the same questions for many people.
How are dioxin levels measured?Dioixn levels are usually reported as a toxic equivalents or TEQs. We multiply concentrations of 17 different dioxins and furans by a factor based on how toxic each one is compared to the most toxic one. Then the concentrations are added together. So the number reported represents a mixture.
What were the levels found in the study?The soil dioxin levels we found ranged from 0.8 to 76.3 parts per trillion (ppt) TEQ. Of the 85 total samples, 45 were below 11.1 ppt. TEQ. So why is 11.1 ppt important?
Using 11.1 parts per trillion as a point of comparisonThe 11.1 ppt is what we call the “Method B” direct contact value for protection of human health. In this case of dioxins, direct contact means accidental ingestion of soil. Based on risk calculations, exposure to soil with 11.1 ppt dioxins TEQ increases cancer risk by one-in-a-million.*
Using our state cleanup regulation, Method B values can be calculated for many common contaminants, including dioxins. Depending on the situation, they can be used to set cleanup levels. However, we have not done enough evaluation to know what cleanup levels would be appropriate for Rayonier’s contamination. In this case, we are using 11.1 ppt just as a comparison point.
*There is a direct relationship between cancer risk and soil dioxin level, so 22.2 ppt is a two-in-a-million additional risk, and so on.
What do soil dioxin levels in Port Angeles mean for my health?
We did not design this study to assess health risk from exposure to soils. To do that, we would need to look at areas where people could be exposed, like gardens or play areas. However, at the levels we found, we did not feel that it was necessary to take immediate action.
If you are concerned about your soil, there are several things you can do. The greatest exposure risk for soil is accidental ingestion and not skin contact. This means that things like hand-washing and keeping dirt out of your home are very effective. With any soil contaminant, children are the most vulnerable because of their small size, developing bodies, and behaviors like putting their hands in their mouths. See page three of the fact sheet for a list of tips.
For more information on dioxins, please visit the Toxic Substances Portal (Agency for Toxic Substances and Disease Registry)