University of Delaware
Matt Limmer has been awarded a USDA fellowship to study uptake of organic forms of arsenic in rice.

Inorganic vs. organic

UD postdoctoral researcher receives USDA grant to study arsenic uptake by rice


8:34 a.m., Jan. 26, 2016--The University of Delaware’s Matt Limmer has been awarded a two-year United States Department of Agriculture (USDA) Post Doctoral Fellowship to study uptake of organic forms of arsenic in rice. 

Limmer is a postdoctoral researcher in the laboratory of Angelia Seyfferth, assistant professor in the Department of Plant and Soil Sciences in UD’s College of Agriculture and Natural Resources.

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He said working with Seyfferth is a great benefit because she previously has examined inorganic forms of arsenic, while his interest is in the organic forms. 

“Arsenic exists in a few chemical species. Inorganic forms include arsenite and arsenate. The prevalence of each species depends on the system redox [reduction-oxidation reaction] chemistry,” said Limmer. 

The inorganic forms of arsenic have an arsenic atom surrounded by oxygen atoms while the organic forms replace one or more of the oxygen atom(s) with a methyl group. 

“It’s similar to mercury and methyl mercury. You might remember in high school playing with liquid mercury metal. Mercury metal isn’t all that dangerous, but the methylated form is quite a bit more dangerous. A small amount of methyl mercury would easily be absorbed through your skin, potentially with lethal effects,” said Limmer. “Arsenic is a little bit different. The inorganic forms are quite a bit more toxic than the organic forms and so it’s useful to know what’s happening with these different species of arsenic because they have different toxicities.” 

It is also important to distinguish between the organic and the inorganic forms of arsenic to understand the form of arsenic that is present in foods like rice.

“Right now, if you ask people how much arsenic is in their rice, they’ll just give you the total, which isn’t all that useful because you don’t know if it’s a ‘good’ form of arsenic or a ‘bad’ form,” Limmer said. “It’s been only recently that people have started to study in more detail how the organic forms and inorganic forms get into the plants and where they go and how to measure them.” 

Limmer noted that even the good form of arsenic is still not “good” in the traditional sense. “It’s the lesser of two evils, or three evils, or four evils,” he said. 

Using the rice paddies at the college’s Rice Investigation, Communication and Education (RICE) Facility, as well as growing plants in a greenhouse, Limmer will investigate if silicon, which has been studied to see if it can slow down the inorganic forms of arsenic from getting into the rice, can also slow down the organic forms of arsenic that may use some of the same transporters as their inorganic counterparts.  

“Part of the proposal was, ‘Does silicon also affect the uptake of these organic arsenic species?’ And we’ve done some preliminary experiments and that seems pretty promising,” said Limmer.

Limmer, who did his undergraduate work in mechanical engineering with a minor in horticulture at Ohio State University and went on to get his master’s and doctorate in environmental engineering at Missouri University of Science and Technology, said he was interested in finding a post-doctoral program that was food-oriented but also allowed him to work with plants and contaminants. That’s how he came across Seyfferth’s lab. 

“Food is the new cool thing to be studying, given the potential for chemical contaminants. Arsenic in rice is an important topic and Angelia is someone with extensive expertise in the field,” said Limmer. 

Limmer hopes to one day become a faculty member himself and said that working with Seyfferth has been a great learning experience. 

“She is super friendly and helpful and encouraging, and those are all qualities you want in an adviser,” he said.

Article by Adam Thomas

Photo by Wenbo Fan

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