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Princeton geochemist Satish Myneni has shown that ordinary leaf mulch contains chlorinated compounds that were previously thought to come only from pesticides and other man-made pollutants. Future studies will reveal whether these natural compounds are toxic, as are many of the man-made forms.

Photo: Denise Applewhite

What is mulch leaving behind?
Study finds that decaying leaves contain chemicals in same class as DDT and PCBs

by Steven Schultz
It has always seemed so natural: Autumn leaves turn beautiful colors, fall to the ground, then decay into the rich mulch that gardeners prize as the ultimate nourishment for a new season of plant life.

A study by Princeton geochemist Satish Myneni, however, has revealed a new side to this ageless cycle. As leaves and other plant materials die and decay, they naturally develop increasing concentrations of chemicals that, while possibly harmless, belong to the same class that includes the toxic pollutants DDT and PCBs.

In an article published in the Feb. 8 edition of Science, Myneni reported that common leaf mulch from around the world contains high concentrations of chemicals called organochlorines, which were previously believed to come only from pesticides and other man-made products. Earlier studies by other researchers had found some natural organochlorines, but they were not thought to be a ubiquitous part of the ecosystem.

In an accompanying perspective article, William Casey of the University of California-Davis called Myneni's work a "stunning result" with "important social and scientific implications."

Click here for the complete story in the Weekly Bulletin.