ARSENIC IN RICE
Naturally-occurring arsenic in Bangladesh’s groundwater has been identified as one of the world’s great humanitarian disasters. Millions of people are at risk of cancers and other diseases from eating rice irrigated with water contaminated with the extremely toxic arsenic compounds. Arsenic exists in both an organic and an inorganic form, with the latter being the most toxic when consumed. Compared to other foods, rice shows higher levels of inorganic arsenic. This is due to the plant and grain readily absorbing arsenic as the rice plant grows. The current scientific thinking is that no arsenic exposure or intake is safe, but an “acceptable risk threshold” of 1 in 10,000 for an arsenic-induced cancer is generally viewed as sensible and achievable. Based on modest rice consumption by an adult, this would correspond to a concentration of 100 parts per billion (ppb); the equivalent of a grain of rice in about a quarter of a ton of rice.
What is being done?
The University of Massachusetts Amherst analytical chemist Julian Tyson believes that one of the first steps in trying to make a difference and help people avoid this exposure is to increase access to detection and remediation of arsenic-contaminated water. Therefore, Tyson and his students have partnered with Chemists Without Borders to develop a relatively inexpensive, easy-to-use test kit to measure arsenic in Bangladesh’s rice supply, offering both consumers and producers reliable information on exposure. This test-kit is based on quantifying the yellow/brown colored product of the reaction between arsenic hydride (arsine), generated by a suitable reaction in solution, and solid mercuric bromide on a test strip.
Tyson’s students have been conducting experiments to adapt an existing arsenic water test kit for testing rice samples. The idea is not only to provide an accurate and reliable kit, but to teach chemistry students in Bangladesh who have access to a basic lab at the Asian University for Women (AUW) in Chittagong, to use it. These young interns will then provide arsenic exposure information and education on protective measures such as extra washing or choosing different varieties, to local farmers, families, merchants and consumers. In fact, the goal of this program of measurement and education is to create more awareness and help make a significant difference to the people of Southeast Asia in the long run.
All rice contains four bioavailable arsenic compounds: two inorganic oxyanions (arsenate and arenite), and the mono- and dimethyl derivatives of arsenate. The inorganic compounds are human carcinogens; the other two, although not innocuous, are not. One of the key challenges in testing rice instead of water is that starch in the grain interferes with the reaction. One approach is to modify the chemistry by replacing zinc, the hydride-generation reagent, with borohydride. This approach is an adaptation of the procedure described by Bralatei et al.  for the Hach EZ test kit for the determination of inorganic arsenic in water to the determination of inorganic arsenic in rice. There are four crucial stages in the process;
1. extraction of all of the inorganic arsenic from the rice into solution,
2. generation of arsine,
3. its removal from solution,
4. and its reaction with the mercuric bromide crystals on the test strip to give the yellow/brown coloration whose intensity can be related to the concentration of arsenic in solution.
Ideally, all of these processes should be 100% efficient. Initially, the reaction with sodium borohydride was the arsine generation reaction of choice. However, the rate of reaction needed to be slowed down as any arsine generated escaped before the lid with the test strip could be secured, and the borohydride reacted with the acid (and decomposed) before it could be mix with the remainder of the solution. Initial work with perforated gelatin capsules containing solid reagent looked promising, but these were superseded by an agar gel in which borohydride is stabilized with sodium hydroxide solution. Most recent work indicates that superior performance is obtained if the gel contains a small proportion of xanthan gum. Results with these X-BAGS (xanthan borohydride agar gels) have been presented in a Chapter in Mobilizing Chemistry Expertise To Solve Humanitarian Problems . Students at a local high school (Four Rivers Charter School, Greenfield, MA) have been helping with the agar gel development, and undergraduates in a course-based research experience, associated with honors freshman chemistry, have shown that a double teabag functions a lot like an agar gel, opening up a new line of investigation. The test kits made by Industrial Test Systems, some of which have detection limits up to 30-times lower than those currently used, are also being considered.
Problems still to be overcome are;
1. the excessive foaming caused by the co-extracted matrix components
2. and the poor response of the test to low concentrations in solution due to the high dilution inherent in the extraction step.
Finally, the method needs to be validated against a reliable instrumental procedure.
If you have an input kindly direct your replies to Julian Tyson (email@example.com)
1. If anyone knows of effective, low-cost, antifoaming agents, we would be interested to hear from you.
2. One can buy pure sodium borohydride tablets and caplets (about 1 g each), but the Arsenator tablets weigh about 4.5 g and contain about 450 mg of sodium borohydride. If anyone knows (a) where such tablets can be obtained, and /or (b) what the filler material is, we would very much like to hear from you.
Once these challenges are solved, the plan is to replace what is now a naked-eye evaluation of color on the arsenic test strip with a method that creates a digital image, for example with a cell phone camera, for analysis.
With this new kit at the hands of the college interns in Bangladesh, Chemists Without Borders will help the interns to develop presentations about the health hazards of arsenic in rice at high schools and community centers. We believe that these young agents of change can bring awareness and education to help people reduce their exposure. With the Arsenic in Water Project already gaining momentum in Bangladesh this kit can truly help to make a difference in Bangladesh.
Since there are different water levels or aquifers have different arsenic contamination, and it is often possible to find a shallower or a deeper one that is relatively free of arsenic. Using that water to irrigate rice can reduce arsenic contamination, as can rinsing rice before cooking, and cooking in excess water. Armed with local test results, locals can make informed decisions about reducing arsenic intake, especially by infants and small children.
We need to address the problems at the village level, and the place to start is with accurate chemical measurement.
Hayley Bennett, “A poison in your pilau,” Chemistry World, 22 August 2017, https://www.chemistryworld.com/feature/arsenic-and-rice-a-growing- problem/3007811.article
Dr. Julian Tyson
Tel: +1 413-545-0195
1. Bralatei, E., Lacan, S., Krupp, E. M., & Feldmann, J. (2015). Detection of inorganic arsenic in rice using a field test kit: a screening method. Analytical chemistry, 87(22), 11271-11276. (doi 10.1021/acs.analchem.5b02386).
2. Julian Tyson, Ishtiaque Rafiyu and Nicholas Fragola, Development of a Test-Kit Method for the Determination of Inorganic Arsenic in Rice, Chapter 5, pp 63-81, in Mobilizing Chemistry Expertise To Solve Humanitarian Problems Volume 1, Editor(s): Ronda L. Grosse, Volume 1267, (web) October 23, 2017. (doi 10.1021/bk-2017-1267.ch005). https://pubs.acs.org/doi/abs/10.1021/bk-2017-1267.ch005