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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