Common water contaminants include particulates, dissolved ions, organic compounds, gases, minerals and microorganisms. Each impurity carries its own risks to biological and chemical research, the quality of pure water and the life of a laboratory’s water purification system.
Suspended particles (1-10µm)
Relatively large suspended particles of sand, silt, clay or vegetation between 1 and 10µm cause turbidity in water and settle to the bottom with gravity. Suspended particles can foul reverse osmosis membranes, filters and chromatography columns. This is particularly relevant if the system is fed from a reservoir or tank within the building.
Colloidal particles (0.01-1.0µm)
Unlike suspended particles, colloids are only 0.01 - 1.0 µm in size and do not settle. Either organic or inorganic colloidal particles can clog filters and foul RO membranes. Colloidal particles interfere with analytical techniques and bypass ion exchange resins causing lower resistivity in deionised (DI) water.
Dissolved inorganic ions
Dissolved inorganic ions include silicates, chlorides, calcium, magnesium, phosphates, fluorides, bicarbonates, sulphates, nitrates and ferrous compounds. High quantities of ions will increase conductivity and reduce resistivity. The resulting instability in laboratory water can negatively influence biological and chemical reactions, reducing the formation of protein-protein and protein-lipid interactions, retarding cell and tissue growth, and altering enzymatic activity. The deionising cylinder or cartridge life in a water system is also adversely affected by inorganic ions.
Dissolved organic compounds
Dissolved organics in water derive from plant or animal decay, and human activities that introduce proteins, alcohols, chloramines, pesticides, herbicides and detergents into the environment. By supporting the growth of microorganisms, dissolved organics interfere with high performance liquid chromatography (HPLC), gas chromatography and fluoroscopy. Other problems caused by organics in water purification systems include poor detection, reduced sensitivity and reproducibility, coating of reactive surfaces, chemical interference, dispersive or non-dispersive effects and fouling or separation of purification media including ion exchange resins.
Water contains naturally dissolved carbon dioxide, nitrogen and oxygen. These dissolved gases can alter the pH of laboratory water and upset ionic balance. Oxygen and nitrogen concentrations can alter the rate of biochemical reactions and high concentrations of dissolved gases can result in bubble formation, hampering flow through chromatography columns and micro-channels, as well as impacting on spectrophotometric measures. Dissolved carbon dioxide will raise the acidity of water and reduce the capacity of ion exchange resins in DI systems.
Bacteria, fungi and algae interfere with sterile research applications. Bacteria will compete at enzyme-active sites on substrates and adversely influence cell and tissue culture. Free-floating bacteria can form biofilms on surfaces which can be difficult to remove. Continuing to grow for several years, biofilms will unpredictably release bursts of bacteria and their associated endotoxins and nucleases. Nucleases will break down DNA and RNA in samples whilst endotoxins affect cell growth and function. Microorganisms are also known to block filters in water purification systems.
Endotoxin-free or pyrogen free water is required for mammalian cell cultures, as well as for the rinsing or preparation of solutions or devices that will have further contact with humans or other mammals. The major and most significant component of endotoxins is lipopolysaccharides (LPS) derived from Gram negative bacteria walls. Introduction of LPS into the blood or spinal fluid causes toxic responses and induces the development of fever (i.e. a “pyrogenic” effect). The words endotoxin and pyrogen have become used in a wider sense to designate the active LPS molecules. In high purity water, potentially pyrogenic substances are predominantly endotoxins. Both terms endotoxin-free and pyrogen-free water are used therefore to designate water free of LPS.
RNase and DNase are naturally occurring enzymes that are instrumental in regulating bodily functions. As important as these are to the life process they can be devastating to nucleic acid experiments. If these contaminants are present in the pure water used, the ability to amplify DNA molecules will be severely limited. Likewise, experiments utilising RNA can be disrupted.
Viruses are considered to be non-living nucleic acids which can adversely affect cell and tissue growth. It is therefore necessary to remove them from water where the application demands.