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Small-scale Zhang, Crain study misses the mark

November 28, 2008  - By

By: Rick Doyle, Synthetic Turf Council

A couple of publications have reprinted information from a small scale study conducted by Drs. Zhang, Han and Crain, which first appeared in the Journal of Exposure Science and Environmental Epidemiology, that concluded synthetic turf contains hidden toxins. While well-intentioned, the study presented information that was flawed and misleading.

Because the public turns to the Synthetic Turf Council with their questions, we feel it is important to provide context and clarification about this information.

The study made several conclusions about synthetic turf:

  • Rubber granules contained PAHs at levels above health-based soil standards.
  • Zinc contents were found to far exceed soil limits.
  • The analysis of one artificial grass sample showed a slightly worrisome chromium content and high bioaccessible fractions of lead in both synthetic gastric and intestinal fluids.
  • PAHs had low bioaccessibility.
  • Lead contents were low in all the samples in reference to soil standards. However, the lead in the rubber granules was highly bioaccessible.

One of our primary concerns is that the authors did not use the fundamental principles of what scientists refer to as “experimental design” in conducting their study. Conclusions were made from single sample data without the use of multiple or repeat samples from the same field. Use of repeat samples is a fundamental statistical approach, and is routinely used to ensure that test conclusions are statistically valid. This basic scientific methodology was not followed. Therefore, the study’s final conclusions should be discounted.

Another concern is that the study uses an inappropriate measure for evaluating the concentrations of metals in the few samples it tested. The study used soil standards because there are no health-based standards for rubber infill — but rubber is fundamentally different than soil. No basis for correlation is given or suggested; therefore, the conclusions stating rubber granules and zinc contents in synthetic turf exceed soil standards are misleading at best.

The fact that soil and rubber infill are fundamentally different is confirmed in a letter from the NY State Department of Environmental Conservation: “Exposure evaluation for the crumb rubber in your product [artificial turf athletic fields] is different than exposure evaluation for soil. Comparison of the Department’s Soil Clean-up Objectives to an analysis of components of synthetic turf would serve no useful purpose….therefore, use of the clean-up objectives as a measure of your products acceptability, or its effect on the environment, would not be appropriate.”

Finally, the article misleads readers in its references to bioaccessibility and bioavailability, and quotes Zhang as stating that the study does not provide bioavailability data, which is critical to understanding the true human health risk. If the study is little more than a solubility test, one has to wonder how the “results” are relevant. In addition, intestinal bioaccessibility for crumb rubber lead is zero, but this result is not discussed.

The synthetic turf industry is proud of its unblemished record of human health and environmental safety since synthetic turf was first introduced more than 40 years ago.

We’ve worked hard with scientists, governmental agencies and other reliable resources to validate the safety of synthetic turf, and dispel misinformation. We will continue to make sure the public is presented with the truth about synthetic turf.

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