Tuesday, November 17, 2015

Natural pesticides from a common weed launched Kaua`i's pesticide furor

(Note: A version of this article appeared Nov. 17, 2015, in Honolulu Civil Beat.) 

The plant blamed for much of Kaua`i’s pesticide furor is a medicinal, edible shrub with a truly awful smell. 

It flowered again recently, sending across the West Kauai landscape a rank stench which, in susceptible folks, can cause teary eyes, headaches and nausea.

West Kauai sugar plantation workers call it spiderflower, but it is more often known as stinkweed; its scientific name is Cleome gynandra.

In November 2006, students and staff at Waimea Canyon Middle School complained of a bad smell that made them nauseous and left them with throat irritation, watery eyes and dizziness. Many attributed it to agricultural spraying on a field next to the school. 

It flowered again recently—the same time of the year as the initial 2006 report—and on West Kauai, people were once again complaining about the stench.

(Image: A ratty-looking sample of stinkweed, Cleome gynandra, in a field west of Kekaha on Kaua`i. Credit: Jan TenBruggencate. )

When I heard of the latest stinkweed outbreak in the second week of November 2015, I went to West Kauai and collected samples (in sealed plastic bags) in Waimea, Kekaha and Mana—some on my own and some during a driving tour with Allan Smith and Robin Robinson of Syngenta, a seed company that leases extensive acreage in the area.

(Image: A healthier looking stinkweed photo specimen.  Credit: Forest and Kim Starr.)

One of the things that struck me about the plant is that its smell is so variable. Some specimens smelled not at all. Others were very strong—enough to make you gag. Some had a very intense chemical smell, others a smell similar to the popular local vegetable bittermelon (Momordica charantia). When it was blooming in past years, Robinson said, sugar plantations would sometimes get calls about a petroleum odor, with callers suggesting there must be a fuel spill nearby. 

“I can smell the sulfur in it,” said one person I asked to smell the plant sample in one plastic bag. “But this sample over here smells almost good.”

This variability is confirmed on the website for Plant Resources of Tropical Africa, which says people who grow it commercially have difficulty getting consistent results, because of variability in many features of the plant. 

The variability also helps explain why some of the affected individuals at Waimea Canyon Middle School, who said they were familiar with stinkweed elsewhere, insisted that it’s not what they smelled at Waimea.

The Hawai`i Center for Food Safety, in its Pesticides in Paradise report, insists that pesticides and not any plant are to blame: "A teacher...rejected the explanation given by Hawai`i officials and Syngenta that 'stinkweed' was he culprit, saying she was familiar with stinkweed's odor and that was not the cause."
The flowering alone can release a strong odor, but if the plant is rubbed or crushed, or if a field of stinkweed is plowed, the stink can be overpowering. One of the reported incidents at Waimea Canyon Middle School occurred while the plant was flowering, another while the stinkweed-infested field was being tilled, Robinson said.

Waimea Canyon Middle School was impacted several times from 2006 to 2008 with the odor that apparently blew in from a neighboring field. Many of the teachers and parents of impacted students blamed agricultural spraying on nearby fields. 

The much-criticized CFS report argues that "Communities in Hawai`i are rightly concerned about pesticide drift that occur from open-air GE seed corn operations. Teachers and schoolchildren in Waimea on Kaua`i became sick on at least three separate occasions following chemical applications to a nerby seed corn plot...

"In a 2008 episode, 60 children and at least two teachers experienced headaches, dizziness, nausea and/or vomiting; 10 or more children were treated at an emergency room, several were put on a nebulizer to relieve respiratory distress and one as given an anti-vomiting medication intravenously."

The state commissioned a study by Qing X. Li, Jun Wang and Robert Boesch, of the University of Hawai`i’s Department of Molecular Biosciences and Bioengineering. Their findings, which are rejected by some of the affected school folks, concluded that spiderflower/stinkweed is a powerful chemical factory.

“A closed chamber laboratory air emission study identified 29 chemicals (some with insecticidal activities) produced by stinkweed,” they said in their report. When they compared that with air samples in the field, they found all 29 chemicals in the air. When they tested the air at the school—indoors and outdoors—they found about half of those chemicals.

The chemical that the scientists felt was likely most at fault is a natural, plant-based compound called methyl isothiocyanate (MITC), an organosulfur compound. Their studies showed it is significantly higher in concentration in flowers and seed pods than leaves and stems of the stinkweed.

“MITC is a highly foul-smelling, noxious chemical at high concentrations, and is cited as a potent lachrymator (eye irritant) and nose and throat irritant. Besides MITC, other stinkweed derived compounds found during this study are also known potential irritants,” they wrote.

The studies also found residues of five known pesticides. When they did the air quality testing, they found that “Concentrations of the pesticides and MITC were well below health concern exposure limits or applicable screening levels.”

The plant has been in the Hawaiian Islands for more than 150 years, having first been observed in 1857. It is on all the main islands, sometimes known as honohina, `ili`ohu, wild spiderflower or spiderwisp. It is native to central America, from Texas south to Argentina, according to the Manual of the Flowering Plants of Hawai`i.

It has spread around the world, a weed in some areas and a cultivated plant in others. The leaves are eaten in Africa and parts of Asia, although it must be cooked. One Thailand website warns that cooking, drying or fermentation reduces the levels of hydrocyanic acid, which it says is toxic to central nervous system. 

The plant is attractive to some insects; repellent to others. In some areas it is used as a mosquito and tick repellent, but when I viewed it on West Kaua`i, many species were severely infested with
It seems to do best after a rain in the drier parts of the Islands. It is recognized by a 5-part leaf (sometimes 3 or 7), long narrow seed pod, and small white flowers that have long spidery parts extending beyond the petals.

It is in the Capparaceae family. A native Hawaiian plant in the same family is maiapilo or pua pilo.

© Jan TenBruggencate 2015

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