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Table 3 Associations between nitrate in community water systems and demographic, land use, and water system characteristics

From: Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water?

Variable

Nitrate concentration

Likelihood of high nitratea

Percent change (95% CI)

p-value

Percent change (95% CI)

p-value

Percent Black, non-Hispanicb

−1.3 (−1.5, −1.0)

< 0.0001

−4.3 (−5.7, −2.9)

< 0.0001

Percent Hispanicb

1.8 (1.6, 2.0)

< 0.0001

1.9 (1.4, 2.4)

< 0.0001

Percent povertyb

−0.8 (−1.2, −0.3)

0.0004

−2.2 (−3.7, −0.7)

0.004

Percent home ownershipb

--f

 

−0.7 (−1.9, 0.4)

0.214

Percent urban householdsb

0.0 (0.0, 0.1)

0.14

0.4 (0.2, 0.6)

< 0.0001

System size: Smallc

9.0 (4.6, 13.7)

< 0.0001

−21.8 (−31.6, −10.5)

0.0003

System size: Mediumc

15.8 (9.2, 22.8)

< 0.0001

−24.8 (−40.4, −5.1)

0.016

System size: Largec

36.2 (27.1, 45.9)

< 0.0001

−10.0 (−30.6, 16.7)

0.426

System size: V. Largec

51.0 (28.2, 77.9)

< 0.0001

54.1 (−20.4, 199)

0.200

Source water: Groundwaterd

33.9 (26.4, 41.9)

< 0.0001

311 (201, 460)

< 0.0001

Percent croplandb

0.6 (0.5, 0.8)

< 0.0001

3.3 (3.0, 3.7)

< 0.0001

Livestock per 100 acresb

0.1 (0.0, 0.2)

0.008

0.2 (0.0, 0.5)

0.107

Region: Northeaste

84.0 (6.0, 219)

0.030

69.1 (−41.7, 390)

0.333

Region: Southe

58.5 (−1.7, 156)

0.059

106 (−18.5, 418)

0.127

Region: Weste

88.1 (13.9, 211)

0.014

270 (44.7, 849)

0.006

  1. Notes: Percent change in nitrate concentration and likelihood of exceeding 5 mg/L associated with a one-unit increase in the county-level demographic data (e.g., 1% increase in percent Hispanic) and agricultural land use data, and for each system size, region, and source water categories relative to the referent group
  2. N = 39,466. Models include state-specific random intercepts and a fixed intercept term
  3. aLogistic regression; outcome coded as “1” if system-average concentration ≥ 5 mg/L and “0” otherwise
  4. bContinuous predictor, table estimates reflect effect of one-unit change in the predictor
  5. cReferent group: very small systems. dReferent group: surface water. eReferent group: Midwest
  6. fNot included in final model
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Environmental Health

ISSN: 1476-069X