Nitrates
Levels of nitrate in groundwater are usually higher than in surface water
conservatively high USGS estimate of baseline groundwater concentration
= 3 mg/L
in 1/3 of US counties tested, 25% wells were above that baseline level
in 5% " " " " , 25% " were > federal water
quality criteria = 10 mg/L
highest concentrations in US well waters > 100 mg/L
Concerns
Human health
- infant methemoglobinea (blue-baby syndrome)
- oxygen carrying capacity of hemoglobin is blocked
- requires relatively high levels of nitrate (10 to 100 mg/L)
- reported cases (<< actual cases)
- worldwide (1945-1994) ~3,000 (some fatalities)
- Hungary (1976-1982) > 1,300 (well water > 22 mg NO3 / L)
- susceptibility of infants
- infant stomach is less acidic than adult stomach
- complete conversion of nitrate to nitrite by bacteria
- infant hemoglobin is more susceptible to conversion to methemoglobin
- infants consume 10x more water per body mass than adults
- other groups at risk
- pregnant women
- increase in methemoglobin from 1% to 10% @ thirtieth week
- cancer patients
- hemoglobin is especially sensitive
- people with reduced stomach acidity
- Potential carcinogenicity
- formation of nitrosamines
- humans are capable of converting nitrosamines
- metabolic intermediate that alters DNA
- associated with digestive tract cancers
- > 300 nitroso compounds tested
- > 90% carcinogenic to every species tested
Environmental
- nitrogen as a limiting nutrient
- ->algal blooms (fresh water & enclosed embayments)
- noxious species (e.g., blue green algae)
- eutrophication anoxia fish kills
- ->coastal waters ????
- algal blooms (dinoflagellates)
- planktonic toxins (e.g., paralytic
shellfish poisoning or PSP)
