‘Safe’ water in Bangladesh wells may be loaded with arsenic

A family collects water from a smaller community safe drinking water device. (Credit: R. Reddy)

New research raises serious concerns with the performance of some arsenic test kits commonly used in Bangladesh to monitor water contamination.

Researchers tested eight commercially available arsenic test kits, and found that several—including the most widely used in Bangladesh—performed poorly.

“The implication is that well waters could have arsenic well above the safe drinking water limit, even though the test result says the level is much lower and safe,” says Kim Hayes, professor in civil and environmental engineering at the University of Michigan and a lead author of the paper in Water Research.

“These findings point to the need for manufacturers to ensure the accuracy of kits, and in particular, that the calibration color charts provided are consistent with the kit performance.”

A research uses a testing kit to check for arsenic in water in a beaker
A graduate student tests well water in Chanda village in Southwest Bangladesh. (Credit: R. Reddy/U. Michigan)

How much arsenic is really in the water?

Arsenic in water is a long-standing problem in Bangladesh. About 25 million Bangladeshis face serious risks of developing skin lesions and cancers due to unsafe levels of arsenic in drinking water.

Testing water quality and sharing the results with residents has been one of the most effective interventions for reducing the number of households consuming arsenic-contaminated water.

In rural arsenic-affected locations, government agencies and nongovernmental organizations often rely on field-test kits to monitor drinking water quality. Raghav Reddy, who recently received his doctorate in environmental engineering, learned through conversations with local users of field-test kits that some had concerns about the kits’ accuracy.

This led researchers to test eight commercially available arsenic field-test kits from Hach, Econo Quick, Econo Quick II, LaMotte, Quick, Quick II, Wagtech, and Merck. To assess test kit accuracy, the researchers compared results with arsenic measurements from an established laboratory method (hydride generation atomic absorption spectroscopy, HG-AAS) using certified arsenic standards.

The researchers ran more than 300 arsenic test kit measurements across 21 different water samples in Bangladesh and 14 different test kit boxes of eight commercial products.

For a subset of water samples, they also presented completed test strips to a five-person panel consisting of government and NGO employees who regularly use arsenic field-test kits. Panel comparison of the test strip color to calibration color blocks allowed an assessment of the variability of color matching from eye by expert users.

A person holds a test strip labled "9A-C" with a yellow dot at the end up to a chart showing light to dark colored dots indicating different levels of arsenic in water
After a series of steps with different chemical reagents, testers check the color that develops on a test strip is against a reference chart provided by the kit manufacturer. A darker color indicates a higher concentration of arsenic in the water sample. (Credit: R. Reddy/U. Michigan)

Finally, they used a color scanner to eliminate user-dependent color matching errors to assess the accuracy and precision of each kit. The most accurate kits returned field-test values closest to lab-tested arsenic values. The most precise kits were highly consistent when repeated.

Two kits (LaMotte and Quick II) provided accurate and precise estimates of arsenic; four kits (Econo-Quick, Quick, Wagtech, and Merck) were either accurate or precise, but not both; and two kits (Hach and Econo-Quick II) were neither accurate nor precise.

The Hach and Econo-Quick kits are the two most widely used field kits in Bangladesh today. The Hach kit results varied between replicate measurements and always underestimated arsenic levels across the range of concentrations tested. The Econo-Quick kit showed good repeatability between replicate measurements but tended to overestimate arsenic by a factor of two.

3 recommendations

Arsenic detection for all kits in this study is based on the Gutzeit method, in which arsenic species form a colored complex on a paper test strip with color intensity proportional to arsenic concentration in water samples. The manufacturers provide a color calibration chart for manual color matching.

“Simply put, the Hach test strip colors are too light, in comparison to the darker color block charts provided by the manufacturer, for a verified arsenic concentration in laboratory measurements, while the Econo-Quick test strips are too dark,” Hayes says.

“Particularly worrisome are kits that produce lighter color test strips than they should. Such an underestimation of arsenic means a well might be labeled as meeting a safe water quality standard when in fact it does not. Our results mean that individuals could be drinking and cooking with arsenic-contaminated water while believing it to be safe because of faulty test kits.”

The study provides three recommendations: kit manufacturers should address reported inaccuracies; decision-makers should carefully evaluate their use of field kits for arsenic measurements; and kit users should conduct quality control checks to identify potentially erroneous results.

Additional researchers from Asia Arsenic Network, an NGO in Bangladesh, the University of Colorado, CIRES, and the University of Michigan. The Graham Sustainability Institute and the University of Michigan supported the work.

Source: University of Michigan