Cadmium in Water Water Purification System

Cadmium as a Water Contaminant

Cadmium (Cd)
Cd2+
Cadmium occurs naturally in zinc, in lead and copper ores, in coal and other fossil fuels, in shales
and is released during volcanic action. These deposits can serve as sources to ground and surface
waters, especially when in contact with low total dissolved solids (TDS) and acidic waters. Major
industrial releases of cadmium are due to waste streams and leaching of landfills, and from a variety of
operations that involve cadmium and/or zinc. These may include many different types of industrial
operations.
Cadmium is found in drinking water supplies as a result of deterioration of galvanized plumbing,
along with industrial waste contamination, or surface water contamination by certain fertilizers…
Although it is possible for trace cadmium to be chelated or sequestered as with any metal, it will
generally be found in the dissolved ionic form.
Food is the major source of cadmium in Humans. Leafy vegetables contain approximately 0.05 –
0.12 mg cadmium/kg.

Sources of Contaminant:
Corrosion of galvanized pipes
Erosion of natural deposits
Discharge from metal refineries
Runoff from waste batteries and paints

Potential Health Effects:
Short Term – nausea, Vomiting, diarrhea, muscle cramp, sensory
disturbances, liver injury, convulsions, shock and renal failure.
Long Term – kidney, liver, bone and blood damage.

Treatment Methods
Coagulation/Filtration, Ion Exchange, Lime softening, Reverse Osmosis,
Distillation.

Health Effects
The US EPA has established a Maximum Contaminant Level (MCL) of 0.005 milligrams per liter
(mg/L) for cadmium in drinking water. The Agency has found cadmium to potentially cause a variety of
effects from acute exposures, including: nausea, vomiting, diarrhea, muscle cramps, salivation, sensory
disturbances, liver injury, convulsions, shock and renal failure. Drinking water levels which are
considered “safe” for short-term exposures are: 0.04 mg/L for a 10-kg (22 lb.) child consuming 1 liter of
water per day for one- to ten-day exposures, and 0.005 mg/L for a longer-term (up to 7 years)
exposure.
EPA has established a reference dose (RfD0 for cadmium at – 5×10-4 mg/kg/day. The RfD is based
upon chronic intake that will result in the kidney concentration of 200 µg/g. No-observed-adverse-effect
level (NOAEL) for Cadmium for humans is 0.01 mg/kg/day.
Cadmium has the chronic potential to cause kidney, liver, bone and blood damage from long- term
exposure at levels above the MCL. There is inadequate evidence to state whether or not cadmium has
the potential to cause cancer from lifetime exposures in drinking water.

Treatment Methods
(Residential)
Strong Acid Cation Resin*
Weak Acid Cation Resin
Reverse Osmosis
Distillation
(Municipal)
Strong Acid Cation Resin
Precipitation/filtration
Lime softening

In soluble ionic form, cadmium may be removed from water using standard, strong acid cation
(SAC) resin regenerated with salt (NaCl or KCl). SAC resins have a higher selectivity for cadmium than
hardness, so a whole house softener should perform well to remove cadmium as long as it is
still removing hardness. Care should be taken to avoid operating past the hardness exhaustion by
downgrading the operating capacity by 25%.
For cartridge applications, weak acid cation resins (WAC) in sodium (Na) form will exhibit higher
capacity and selectivity than will SAC resins. WAC resins are effective well beyond the hardness
capacity.
Cadmium can also be removed by coagulation, precipitation and filtration treatment when pH is
raised. It can also be removed as a part of a lime softening process.
Reverse osmosis systems can effectively reduce all ionic species of cadmium by 92-98 percent of
the influent concentration for influent water concentrations up to at least ten times greater than the MCL
when operated at pressures greater than 50 psig and at temperatures between 40° and 85° F. There
are several types of membrane materials in use. Acceptable operating conditions for each type are
different. Care must be taken to insure that operating conditions for the specific membrane material are
adhered to, especially feed water pH, particulates and oxidants, to maintain effectiveness. Periodic
testing for percent rejection should be performed. Another effective means of reducing cadmium is
distillation.
Precipitated and insoluble species of cadmium that may exist in some waters can be reduced with
filtration that effectively removes particles of 0.5 microns in size.
Water sampling and analysis, using recognized analytical procedures to verify performance, are
recommended to assure that the MCL of 0.005 mg/L can be met by the water treatment system at all
operating conditions.

Author

@AngieY

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