From: DCHAS Membership Chair <membership**At_Symbol_Here**DCHAS.ORG>
Subject: [DCHAS-L] Limonene article in CEN
Date: Mon, 18 Mar 2019 08:13:08 -0400
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Message-ID: EEBA4B35-D53D-4B1A-842F-3B6AF6953DD6**At_Symbol_Here**dchas.org


From: Monona Rossol
Re: limonene in CEN

https://cen.acs.org/biological-chemistry/natural-products/chemistry-behind-marigoldspest-control-power/97/i10

A very misleading article on (+)-limonene from marigolds appeared on page 15 of the Chemical & Engineering News, March 11, 2019. The writer notes this chemical was found in the fragrance of marigolds which explains why these flowers keep certain insect pests away from greenhouse tomatoes. The writer doesn‰??t tell us that (+)-limonene has been an EPA-registered pesticide ingredient for decades and it has been long-known that it is not just a repellent, it is a fly killer. I became aware of this fact after a college lab course in which we bred fruit flies was terminated by bending a wee bit of orange peel (full of limonene) above our little containers of critters. Stone cold dead was the almost instant result.

So the most important issue in this experiment was missed, namely that (+)-limonene did not need to be sprayed onto the plants to be effective. Researchers found that only using a vapor dispenser similar to a room deodorizer was enough. This means: 1) huge savings can be realized on the amount of pesticide needed; 2) its well-known adverse (Category 1) aquatic toxicity issue can be easily avoided; and 3) it is possible to target only species that are smart enough to get away from the pesticide before it is lethal to them.

And then there are all the occupational exposure issues this use raises. Any accurate GHS SDS on (+)-limonene will list it as a Category 2 skin irritant and a Category 1 skin-sensitizer. And the DFG-TWA workplace air quality standard is only 5 ppm, above which d-limonene may also be a threat to the fetus. There also is significant anecdotal evidence that it is an asthmagen. That presents some interesting worker protection issues in an enclosed greenhouse environment.

I also would suggest that the chemical should not only be identified as ‰??(+)-limonene.‰?? Make sure readers know this is orange peel oil, citrus oil, d-limonene, dipentene, and so on. This chemical is banned in the E.U. from cosmetics, fragrances, and children‰??s products as any other Category 1 skin-sensitizer would be. Here in the U.S., we have trouble finding products without citrus as a fragrance or ingredient. Which also makes me wonder whether or not U.S. consumers can be included among those those species smart enough to get away from d-limonene before it is harmful to them.

Monona Rossol

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