Risk assessment of nitrate in drinking water

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This is the main page of the WP3.4 assessment of the health impacts of nitrate in drinking water. This and the articles linked to it describe the first pass assessment.

The article of the reporting associated with this assessment (i.e. the deliverable) is located here. The assessment itself is located on INTARESE Mediawiki.

Background material:

• There is considerable general material available on this wiki on the development of the WP3.4 assessment
• The article on the WP3.4 First pass assessment provides an overview of all the assessments grouped under WP3.4
• The models described on this page are Analytica files. While the software is proprietary (i.e. not free), a free viewer (Analytica player) is available in which models can be investigated, and a free trial version is available at the Lumina Decision Systems website.

This is the main page of nitrate risk assessment conducted in INTARESE WP3.4. The analytica file can be uploaded here: File:Nitrate.ANA. Detailed information about nitrates in drinking water is found in INTARESE wiki.

Scope

Purpose

To investigate the effects of nitrate contaminated drinking water.

Boundaries

European countries in selected regions:

• First pass assessment:
  • England and Wales

• Second pass assessment:
  • England and Wales
  • Finland
  • Spain
  • Romania
  • Hungary

• Infants < 6 months of age
• Exposure to nitrate via baby food formula mixed with drinking water and via drinking water (onlt tap water in the first pass asessment)
• Effects: infant methemoglobinemia (iMetHb). More detailed information about methemoglobinemia and other nitrate related health effects is found in INTAESE wiki.

Scenarios

This assessment focused only on the current situation, therefore scenarios are not included in the assessment. In the future the assessment may contain the following scenarios:

• Drinking water source: Tap water or well water
• Increased use of bottled water

For the first pass it was deemed appropriate to carry out a diagnostic assessment i.e. to estimate the scale of the health impacts under present conditions, which in this case make use of 2003 as the baseline year. We also looked at only areas in England and Wales. It was recognised that the causal diagram should be constructed in such a way that the introduction of policy scenarios is possible, since this is intended for the second pass of the assessment. The introduction of such potential policy scenarios would allow the diagnostic assessment to be transformed into a prognostic assessment i.e. a causal diagram which allows the estimation the likely consequences of different policy options, primarly as a basis for choosing between them.

Intended users

• Researchers

Participants

• Researchers at KTL
• Researcher at Imperial College London
• Researchers at London School of Hygiene & Tropical Medicine
• Researchers at Municipal Institute of Medical Research Foundation

Definition

Causal diagram

Detailed documentation of the design, elaboration and construction of the causal diagram to be used in this assessment is given in article found in |INTARESE wiki. The final draft is presented in figure 1. The working Analytica version of the nitrate model File:Nitrate.ANA.

• 

  Figure 1 - Causal diagram for assessment of the impacts of exposure to nitrate due to MetHg

• 

  Figure 2 - Analytica model of nitrate risk assessment

Decision variables

• Drinking water source (population using public/private water supplies)

Indicators

• Health risk estimates for iMetHb
• Excess cases of iMetHb
• Total ingestion of nitrates from drinking water by infacts < 6 months

Other variables

• Nitrate concentration in drinking water
• Exposure of infants < 6 months to water from private supply
• Infection status of infants < 6 months
• Exposure response function for nitrate and iMetHb: Detailed discussion of this can be found in INTARESE wiki

Indices

• Water companies in England and Wales
• Finland areas
• Country
• Water source

Analyses

Calculating from Excess cases of iMetHb the following numbers:

• Min
• Median
• Mean
• Max
• Std. Dev.

Result

Results

Excess cased of iMetHb

Table 1. The statistics of excess cases of iMetHb in areas of England & Wales.

	Min	Median	Mean	Max	Std. Dev.
ang	8.867809212044037e-006	4.061391113443175e-003	0.02337343869768255	1.892149425579965	0.1060866865198681
bou	1.264258480079276e-005	5.507450878951319e-003	0.03915788203147796	5.249792751091034	0.2232809462385913
brw	1.023622522093214e-005	3.344960540405284e-003	0.02964557904501822	7.567374331984166	0.2560871242802423
caw	1.946064511310523e-005	8.213376957683812e-003	0.09998246008478445	26.08618405681051	0.9649362430651229
cho	1.746264594307055e-005	7.222284600542171e-003	0.06949044839531456	14.11870396142145	0.5499575393958024
dcc	3.42947364536083e-007	5.778151857342573e-004	6.324603714728293e-003	1.705328343265988	0.0569490302909804
eas	1.732078733788408e-005	5.190129083836174e-003	0.089872275675275	53.41999591422744	1.695415722382626
ess	8.018438671509409e-006	4.2265545865814e-003	0.0415458461636681	7.959793248888643	0.3298182507946977
fol	1.626624404895984e-005	6.018387806855795e-003	0.04595088119431283	6.518893443585108	0.2812058077037811
har	2.94994115649411e-006	1.092553250692551e-003	5.444152225790545e-003	0.2692497056604518	0.01724920486457077
mik	1.243995186714602e-005	3.901042559119324e-003	0.02406188804455056	1.68527083755716	0.09362049229491935
nor	7.769198071646717e-008	7.789483281972663e-004	4.086088952279674	1909.318907338719	76.96874266415372
nww	4.91760921364792e-007	5.806024666982399e-004	7.375662679320687e-003	3.298694426934227	0.1053064726349943
por	1.442385503381363e-005	6.219738199364088e-003	0.05735705632914733	12.46693356286341	0.4769076386399186
sea	8.983158746683583e-006	3.452941813308403e-003	0.02113995785521237	1.894736772253743	0.09474292873242055
sev	9.588326991895514e-006	3.919891042156178e-003	0.0238756252018221	2.190289321370028	0.1098119202708908
sos	1.056965180799157e-005	4.184076819310528e-003	0.06692869168709101	35.62867227140667	1.143035141888347
sou	1.552953893119461e-005	6.092061118866147e-003	0.07061023584637183	22.054395419779	0.7570041738471152
sww	1.214485825128024e-006	9.675159422252654e-004	9.253383140175247e-003	2.015871283282304	0.0697875763844563
teh	3.176856287625261e-006	1.282996646193179e-003	6.184970762893474e-003	0.285561943563592	0.0202365196419248
tha	1.401062825875818e-005	5.792075310047158e-003	0.04505204211853146	5.321048973144055	0.2657527073878039
thr	1.619256818053273e-005	6.127582834701198e-003	0.0685170439425303	26.77447775480054	0.87556845085848
wes	1.031188044971007e-005	4.218250216579027e-003	0.06484446766822705	11.30081230340598	0.6046026736162651
wrx	2.553192442025077e-006	9.348274561434395e-004	5.303936522605171e-003	0.2979636710887992	0.01779798252133523
yor	1.542246646732499e-006	1.221627677312532e-003	0.03181765999191983	22.5405707234452	0.7132053024923273
Total	2.346740632406462e-004	0.09512908243494794	5.039199141298125	2181.86167178613	86.7971092009012

• 

  Figure 3 - Medians of excess cased of iMetHb in England & Wales

• 

  Figure 4 - Importance analysis of excess cased of iMetHb

The median of excess cases of iMetHb is low (under 0.01 cases for each area), which is due to low consumption of drinking water, a very low background prevalence of iMetHb and low nitrate levels in drinking water.

Conclusions

The results of integrated environmental health impact assessment for nitrate in drinking water causing iMetHb indicate that there is a risk of iMetHb with high levels of nitrate, though the nitrate levels in drinking water in UK are low. The number of excess cases of iMetHb was under one in each of the studied areas. The major sources of uncertainty in the assessment and results were total daily consumption of water by infants, nitrate concentrations in drinking water and background prevalence of iMetHb. The uncertainty of the ERF slope was unknown. Confounding factor of pathogens was excluded from the assessment and should be taken into account in any future assessment.