Types of Contaminants

What are Contaminants?

Any solutes (contaminants) introduced into the groundwater environment. Contamination is the presence of a constituent, impurity, or some other undesirable element that renders something unsuitable, unfit, or harmful for the physical body, natural environment, workplace, etc.

Types of Contaminants:

Six major categories are,  

1. Radionuclides 
2. Trace metals 
3. Nutrients 
4. Other inorganics 
5. Organics and 
6. Biological.

Radionuclides:

• The nuclear fuel industry is the main source of radioactive contaminants.
• Potential sources occur throughout the nuclear fuel cycle.
• During mining when raw ore is processed ²³⁸U, ²²⁹Th, ²²⁶Ra, and ²²²Rn are potential contaminants.
• Fuel fabrication, fuel reprocessing and power-generating facilities are other potential sources.
• Colorado, New Mexico, Utah, Wyoming, Saskatchewan and Ontario are the U producing regions of North America.
• The nuclear industry is very closely controlled and monitored by federal, state and provincial authorities.

Trace metals:

• Trace metals are a natural component of all groundwaters and represent the largest group of elements in the periodic table.
• Additional sources include (1) mining effluents, (2) industrial wastewaters, (3) urban runoff, (4) agricultural wastes and fertilizers, and (5) fossil fuels.
• Some trace metals (B, Cu, Fe, Zn) are essential for health but others have a tendency to accumulate in the body (or bioaccumulate in organisms low in the food chain) from sources at relatively low concentrations.
• The 13 trace metals that make the EPA list of 129 priority pollutants are: Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, Zn. 

Nutrients:

• Nutrients are ions and compounds containing nitrogen and phosphorus.
• The dominant nitrogen species in groundwater in NO₃^- and to a lesser extent NH₄⁺.
• Phosphorus is less important as a contaminant because of its low solubility and tendency to readily sorb onto solids.
• Sources of N and P are largely agricultural including the use of fertilizers and the cultivation of virgin soils (when large quantities of N are released.)
• Sewage (N) and municipal wastewaters (P) are also sources of nutrients.

Other inorganics:

• This group of “contaminants” includes the major ions usually present in groundwater.
• Extremely high concentrations render water unsuitable for human consumption, animal watering and many industrial uses.
• Health related concerns are low for this group of contaminants but high concentrations of Na⁺ can disrupt blood chemistry and lower Na⁺ concentrations may lead to hypertension.
• Fluoride a good example of a trace non-metal contaminant. At low concentrations F^- has the beneficial effect of reducing tooth decay. At higher concentrations (only x5 higher) F^- can lead to serious health problems including goitre and fluoridosis. 

Organics:

• Contamination of groundwater by organic compounds is a consequence of the large number of petroleum products and man-made organics in common use.
• The EPA list of 131 priority pollutants contains 116 organic compounds, 13 trace metals, asbestos and cyanide. Over 90% are organics.
• The EPA divides the organics into four groups based on the methods used for analysis but ultimately the analytical tool is gas chromatography-mass spectrometry (GC-MS):
• Base-neutral extractables (47)
• Acid extractables (12)
• Volatiles (32)
• Pesticides and PCBs (25)

Biological:

• The important biological contaminants are:
  • Pathogenic bacteria (Fecal streptococci, Fecal colliforms, Escherichia coli, Shigella dysenteriae, Salmonella typhi, Vibrio cholerae)
  • Viruses (enteroviruses, hepatitis A virus, polio virus and rotavirus )
  • Parasites (Giardia, Entamoeba, Cryptosporidium )
• The main sources are (1) land disposal of sewage and septic tanks, (2) leachates from sanitary landfills and (3) agricultural wastes.
• The contaminants are particulate rather than dissolved, transport distances are limited and problems tend to be related to localized sources.