A comparison of recent and long-term average measurements of nitrate in drinking water

Abstract

We evaluated the usefulness of a recent measure of drinking water nitrate as a predictor of long -term average nitrate exposure calculated from historic data. Exposure estimates were calculated for 214 study participants who used public water supplies between 1947 and 1980 in Minnesota. Long -term average nitrate was calculated by linking residential histories to historical nitrate data. For recent exposures, we averaged nitrate measurements in 1980, or the next closest year with measurements. The Spearman correlation coefficient for the relationship between the two measures was 0.54 ( 95% confidence interval [ CI ] = 0.44 ± 0.63 ) . Agreement was highest among those residing 34 or more years in their town as of 1980 ( r s = 0.70; 95% CI = 0.55 ± 0.80 ) . These findings suggest that taking into account the study participants' duration of residence may enhance the validity of using a recent measure as an indicator of past exposures.

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

“…Also, it is not always feasible to obtain water from the residence of interest [22], and use of records might allow one to consider past contaminant levels, including those at past residences. The importance of this has been documented [23]. Finally, use of a records-based method might allow a relatively quick and cost-effective study, perhaps without contacting participants.…”

Evaluation of the Webler-Brown model for estimating tetrachloroethylene exposure from vinyl-lined asbestos-cement pipes

“…These results of these studies are similar to ours. For example, Freedman et al evaluated the validity of using nitrate concentrations in public drinking water supplies from a single year to characterize long-term exposure for a case-control study of non-Hodgkins lymphoma and leukemia [ 25 ]. The authors compared long-term average nitrate measurements from 1947 through 1975 to recent measurements from 1980, and found a moderate level of overall correlation (Spearman correlation coefficient was 0.54, 95% CI:0.44, 0.63).…”

Non-Hodgkin's lymphoma and nitrate in drinking water

“…Furthermore, it is important to consider the calendar time period over which average nitrate concentrations are computed, because several factors affect nitrate values in community supplies, including changes in nitrogen fertilizer use over time and changes in the source of a community's drinking water. The residential stability of the study population has also been shown to be an important factor in the correlation between recent and long term average nitrate exposures 3. Substantial misclassification can occur if recent measurement data are used to estimate long term average exposure.…”