An evaluation of semi-quantitative test strips for the measurement of nitrate in drinking water in epidemiologic studies

Abstract

Consumption of nitrate and nitrite is associated with a variety of health outcomes. Commercially available test strips that allow semi-quantitative estimation of these contaminants in drinking water are inexpensive relative to laboratory testing, and are simple to use. To examine the accuracy of a nitrate/nitrite test strip, we recruited Washington State residents to estimate levels of these contaminants in their tap water using these strips, and simultaneously provide a tap water sample for laboratory analysis. Paired results were available from 102 homes. On the basis of laboratory assay, nitrate levels as nitrogen ranged from no nitrate (27%) to 40.5 mg/l (median 0.4 mg/l). Spearman's correlation coefficient between test strip-and laboratorymeasured nitrate indicated moderate precision overall (r ¼ 0.72). Correlation was similar for homes inside and outside city/town limits, but differed by primary source of water for the purveyor indicated by residents (r ¼ 0.72 for groundwater and r ¼ 0.34 for surface water). Seven (7%) participants reported difficulty in distinguishing colors (contaminant levels) when using the test strip; and among the samples with nitrate, the laboratory assay indicated higher nitrate levels than the test strip for 81%. Nitrite was not detected by laboratory assay; in comparison, five (5%) subjects reported any nitrite according to the test strip. Nitrate/nitrite test strips may be useful in some epidemiologic studies, but should be used with caution, preferably as a screening tool or when laboratory assays are not feasible.

“First alert” for Drinking Water Quality: Commercial Water Quality Testing Kits for Community-Engaged Research

“…Previous studies reported the general agreement of nitrate/nitrite test strips with the laboratory analysis data within the concentration range of this study. 26,33,42 Both overestimation 26 and underestimation 26,33,42 were reported previously and the participant's experience level (novice, experienced, expert) can influence the direction of error. 26 The copper test showed no relationship between the measured values and reported values for both test kit groups (Figure 4c).…”

“…Both primary and secondary drinking contaminants identified by the US EPA can be measured by simple manipulations, with the test kits requiring no advanced education. Several studies evaluated the single-parameter test kits and stated the usefulness of this approach for rapid screening of lead, arsenic, − nitrate/nitrite, and pesticides in water. In this study, we evaluated the test kits that can measure ≥4 water quality parameters.…”

Water quality monitoring records for estimating tap water arsenic and nitrate: a validation study

“…It should be noted, though, that the German study implies greater precision than ours because our "gold standard" (laboratory testing) was presumably better than theirs (test strips). We estimate precision of nitrate test strips to be 0.72 [11]. …”

“…Still, the test strip method relies on subjective comparison of the moistened strip to a colour chart. Bias in ORs due to differential measurement error (including away from the null) might occur if the outcome is already known to the person using the strip [11], whereas linkage-based methods can be applied objectively. Further, for some contaminants, including arsenic [21], a test strip or other in-the-field method suitable for study participants does not exist.…”

“…Detailed methods have been described [11]. Briefly, we used an added-digit technique [12] to identify, via telephone, a sample of 156 residences with children in regions of Washington State with varying levels of arsenic and nitrate.…”