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Drinking Water Indicator:
Maximum contaminants level (MCL) violations and mean concentrations
Measure
: Nitrate MCL violations and mean concentrations in community water systems (CWS) in Oregon
Nitrate is the most common contaminant in ground water aquifers worldwide.
Nitrates are nitrogen-oxygen chemical units that combine with various organic and inorganic compounds.
Nitrate (NO
3) originates in drinking water from nitrate-containing fertilizers, sewage/septic tanks and decaying natural material, such as animal waste. As a result of human activities and population growth, nitrates are increasing in water resources.
The greatest use of nitrates is as fertilizer.
Nitrates do not evaporate, are very soluble in water and can easily migrate.
Since they are very soluble and do not bind to soils, nitrates have a high potential to migrate to ground water. Because they do not evaporate, nitrates and nitrites are likely to remain in water until consumed by plants or other organisms.
Nitrate was first identified as a public health threat in drinking water in 1945 when high nitrate levels from private wells were shown to cause methemoglobimia or “blue baby syndrome” in infants who received formula mixed with well water.
Long-term exposure to high nitrate levels in drinking water has been found in some studies to be a risk factor for several types of cancer (such as
gastric, colorectal, bladder, urothelial, brain, esophageal and ovarian cancer, and non-Hodgkin’s lymphoma). However, other studies have found no association.
There also is some evidence to suggest that exposure to nitrates in drinking water is associated with adverse reproductive outcomes such as spontaneous abortion (miscarriage), intrauterine growth restriction, and various birth defects. However, other studies have found no association.
Nitrate regulations became effective in 1992. If nitrate levels consistently exceed the Maximum Contaminant Level (MCL), the community water system must notify the public and possibly provide alternative drinking water supplies. These measures (of community water systems and population served who are potentially exposed to water not meeting MCLs for nitrates) provide simple estimates of the potential for adverse health effects.
The proportion of CWS with any nitrate violations and the proportion of people receiving water from CWS with a nitrate violation were both consistently below 0.5 percent in every year between 2002 and 2007.
More than 90 percent of the population received drinking water with average nitrate levels lower than 1 mg/L, i.e., 10 percent of the MCL, and maximum yearly nitrate levels under 3 mg/L or 30 percent of the MCL.
Table 1:
Annual percentage and number of CWS with any nitrate MCL violations, and number of people served by CWS with any nitrate MCL violations.
Table 2:
Number of CWS and number of people receiving water from CWS with different mean and maximum concentrations, by year
.
Table 3:
Annual mean and maximum nitrate concentrations across CWS and the number of people served, by mean and maximum nitrate concentrations.
Graph 1:
Number of people receiving water from CWS with different mean and maximum nitrate concentrations in 2007. The black bar indicates the maximum contaminant level of 10 mg/L.
Graph 2:
Number of CWS with different mean and maximum nitrate concentrations in 2007.
_________________________________________________________________________________________________
Table 1:
Annual percentage and number of CWS with any nitrate MCL violations, and number of people served by CWS with any nitrate MCL violations.
|
|
Annual percentage and count
of CWSs with any nitrate MCL violation
|
Annual percentage and count of people
served by CWSs with any nitrate MCL violation
|
|
Year
|
Percent
|
(count)
|
Percent
|
(count)
|
|
2002
|
0.2
|
(2)
|
0.2
|
(6,447)
|
|
2003
|
0.5
|
(4)
|
0.1
|
(3,686)
|
|
2004
|
0.4
|
(3)
|
0.3
|
(10,201)
|
|
2005
|
0.4
|
(3)
|
0.1
|
(2,176)
|
|
2006
|
0.2
|
(2)
|
0.1
|
(1,800)
|
|
2007
|
0.2
|
(2)
|
0.1
|
(1,800)
|
___________________________________________________________________________________________________
Table 2:
Number of CWS and number of people receiving water from CWS with different mean and maximum nitrate concentrations, by year.
|
|
|
By Mean Concentration
|
|
By Maximum Concentration
|
|
Year
|
mcg/L
|
CWS
|
People
|
|
CWS
|
People
|
|
2002
|
≤ 1
|
510
|
2,354,764
|
|
489
|
2,156,095
|
|
|
<1-3
|
117
|
161,525
|
|
124
|
264,483
|
|
|
>3-5
|
32
|
19,559
|
|
38
|
56,085
|
|
|
>5-10
|
15
|
6,489
|
|
22
|
61,224
|
|
|
>10-20
|
1
|
1,997
|
|
2
|
6,447
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
|
2003
|
≤ 1
|
530
|
2,386,012
|
|
504
|
1,536,293
|
|
|
<1-3
|
128
|
137,321
|
|
145
|
912,200
|
|
|
>3-5
|
41
|
54,433
|
|
38
|
68,329
|
|
|
>5-10
|
19
|
8,334
|
|
27
|
65,592
|
|
|
>10-20
|
0
|
0
|
|
4
|
3,686
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
|
2004
|
≤ 1
|
549
|
2,372,456
|
|
517
|
1,698,314
|
|
|
<1-3
|
141
|
172,309
|
|
162
|
782,091
|
|
|
>3-5
|
35
|
62,540
|
|
31
|
69,359
|
|
|
>5-10
|
22
|
13,836
|
|
34
|
61,176
|
|
|
>10-20
|
0
|
0
|
|
3
|
10,201
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
|
2005
|
≤ 1
|
543
|
2,429,350
|
|
520
|
2,227,140
|
|
|
<1-3
|
140
|
161,932
|
|
153
|
294,389
|
|
|
>3-5
|
36
|
49,192
|
|
36
|
69,989
|
|
|
>5-10
|
19
|
3,978
|
|
27
|
51,058
|
|
|
>10-20
|
1
|
300
|
|
3
|
2,176
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
|
2006
|
≤ 1
|
529
|
2,436,029
|
|
506
|
2,250,128
|
|
|
<1-3
|
137
|
158,212
|
|
148
|
280,403
|
|
|
>3-5
|
38
|
36,386
|
|
34
|
34,840
|
|
|
>5-10
|
11
|
6,661
|
|
27
|
71,917
|
|
|
>10-20
|
2
|
1,800
|
|
2
|
1,800
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
|
2007
|
≤ 1
|
527
|
2,315,747
|
|
506
|
2,169,304
|
|
|
<1-3
|
132
|
186,529
|
|
140
|
225,340
|
|
|
>3-5
|
41
|
19,018
|
|
45
|
83,665
|
|
|
>5-10
|
13
|
6,401
|
|
21
|
47,646
|
|
|
>10-20
|
1
|
60
|
|
2
|
1,800
|
|
|
>20
|
0
|
0
|
|
0
|
0
|
___________________________________________________________________________________________________
Table 3:
Annual mean and maximum nitrate concentrations across CWS and the number of people served, by mean and maximum nitrate concentrations.
|
|
|
Mean nitrate concentration
|
Maximum nitrate concentration
|
|
Year
|
mg/L
|
CWS
|
People served
|
CWS
|
People served
|
|
2002
|
≤ 1
|
510
|
2,354,764
|
489
|
2,156,095
|
|
|
<1-3
|
117
|
161,525
|
124
|
264,483
|
|
|
>3-5
|
32
|
19,559
|
38
|
56,085
|
|
|
>5-10
|
15
|
6,489
|
22
|
61,224
|
|
|
>10-20
|
1
|
1,997
|
2
|
6,447
|
|
|
>20
|
0
|
0
|
0
|
0
|
|
2003
|
≤ 1
|
530
|
2,386,012
|
504
|
1,536,293
|
|
|
<1-3
|
128
|
137,321
|
145
|
912,200
|
|
|
>3-5
|
41
|
54,433
|
38
|
68,329
|
|
|
>5-10
|
19
|
8,334
|
27
|
65,592
|
|
|
>10-20
|
0
|
0
|
4
|
3,686
|
|
|
>20
|
0
|
0
|
0
|
0
|
|
2004
|
≤ 1
|
549
|
2,372,456
|
517
|
1,698,314
|
|
|
<1-3
|
141
|
172,309
|
162
|
782,091
|
|
|
>3-5
|
35
|
62,540
|
31
|
69,359
|
|
|
>5-10
|
22
|
13,836
|
34
|
61,176
|
|
|
>10-20
|
0
|
0
|
3
|
10,201
|
|
|
>20
|
0
|
0
|
0
|
0
|
|
2005
|
≤ 1
|
543
|
2,429,350
|
520
|
2,227,140
|
|
|
<1-3
|
140
|
161,932
|
153
|
294,389
|
|
|
>3-5
|
36
|
49,192
|
36
|
69,989
|
|
|
>5-10
|
19
|
3,978
|
27
|
51,058
|
|
|
>10-20
|
1
|
300
|
3
|
2,176
|
|
|
>20
|
0
|
0
|
0
|
0
|
|
2006
|
≤ 1
|
529
|
2,436,029
|
506
|
2,250,128
|
|
|
<1-3
|
137
|
158,212
|
148
|
280,403
|
|
|
>3-5
|
38
|
36,386
|
34
|
34,840
|
|
|
>5-10
|
11
|
6,661
|
27
|
71,917
|
|
|
>10-20
|
2
|
1,800
|
2
|
1,800
|
|
|
>20
|
0
|
0
|
0
|
0
|
|
2007
|
≤ 1
|
527
|
2,315,747
|
506
|
2,169,304
|
|
|
<1-3
|
132
|
186,529
|
140
|
225,340
|
|
|
>3-5
|
41
|
19,018
|
45
|
83,665
|
|
|
>5-10
|
13
|
6,401
|
21
|
47,646
|
|
|
>10-20
|
1
|
60
|
2
|
1,800
|
|
|
>20
|
0
|
0
|
0
|
0
|
___________________________________________________________________________________________________
Graph 1:
Number of people receiving water from CWS with different mean and maximum nitrate concentrations in 2007. The black bar indicates the maximum contaminant level of 10 mg/L.
___________________________________________________________________________________________________
Graph 2:
Number of CWS with different mean and maximum nitrate concentrations in 2007. The black bar indicates the maximum contaminant level of 10 mg/L.
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