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Keeping Watch on Water Emerging contaminants in drinking water could be a cause of concern for lab water purification. by Estelle Riche, Ph.D. and Maricar Tarun, Ph.D.
Figure 1. Combination of various purification technologies are being used to remove a wise variety of emerging water contaminants. Click to enlarge. | When the Associated Press published results from a five-month study on the presence of pharmaceuticals in drinking water in 2008, the study made headlines across the country. Drugs such as antibiotics, anti-convulsants, mood stabilizers, and cholesterol-lowering medications were found to be present in the drinking water of more than 40 million Americans.
Previous studies conducted by the U.S. Geological Survey found an average of twenty different drugs in the wastewater streams they examined—everything from caffeine to over-the-counter medications, such as ibuprofen to rare but potent cancer chemotherapy drugs.
In addition to pharmaceuticals, contaminants in drinking water such as perchlorates, pesticides, herbicides, endocrine disrupting chemicals, brominated flame retardants, and personal care products make for a steady stream of news about what is in the water supply.
While such contaminants can be found in drinking water, should they be a concern for researchers? Are these contaminants making their way from the tap into the high-purity water used in the laboratory?
Emerging contaminants
Despite being referred to as “emerging contaminants,” many of these compounds have been in use for decades. Their presence in water is not new. However, the ability to measure these contaminants at the very low concentrations at which they exist in our water supply is new. Analytical laboratories assessing and monitoring the presence of such emerging contaminants must ensure their laboratory water is purified to the highest degree possible, so that even minute amounts of contaminants in the purified water do not interfere with trace level analyses.
Other laboratories that require a similar standard of purity for water are those that develop sensitive methods for the detection of emerging contaminants and their metabolites in various matrices, and those that focus on toxicity testing.
These contaminants may also have an impact on cell-based or other biological assays routinely conducted in research labs. Effects of these contaminants on experimental outcomes may be so subtle, however, that the cause of unexpected results might not be immediately traced back to the water, leading to wasted time and effort in tracking down the culprit.
Millipore monitors reports of emerging contaminants and assesses whether they are effectively removed via the company’s water purification systems or require additional purification steps. Two recent examples include endocrine disrupter chemicals (EDCs) and perchlorate.
EDCs4 are natural and synthetic substances that alter the function of the endocrine system and consequently cause adverse effects in an organism or its progeny. Substances suspected of being EDCs include organohalogens (chloroform, dioxins), chemicals used in pesticides (DDT), and plastics (bisphenol A, phthalates). Research groups are actively designing sensitive analytical methods to identify and quantify EDCs for which high-purity water is a requirement. In addition to EDCs entering laboratory water from the tap, the materials used in the water purification itself may contaminate water due to the use of plastic materials in filtration membranes, resin housings, and piping that may leach EDCs.
Millipore water purification systems are able to remove a variety of water contaminants. As shown in the diagram above, these systems combine various purification technologies, such as reverse-osmosis, electrodeionization, activated carbon, ion-exchange resins and ultra-violet radiation. Various point-of-use disposable cartridges have been designed to answer the needs of scientists requiring water free of specific contaminants. In particular, a cartridge was optimized for EDC removal.
The cartridge is made of materials selected to prevent recontamination of the purified water and contains a specific type of activated carbon. GC-MS analysis showed that water purified using a combination of technologies commonly used in Millipore water purification systems with the addition of the specific carbonaceous POU purifier contains no measurable amounts of EDCs.
Perchlorate is another example of an emerging contaminant. Perchlorate salts are used widely in explosives, solid rocket fuel, matches, and air bags. Perchlorate is chemically inert under most conditions and until recently was not considered to be a hazardous substance; as such, the compound was commonly disposed of through wastewater systems. In the late 1990s, development of a sensitive method for perchlorate detection in ground and surface water showed widespread contamination. The increasing number of environmental laboratories monitoring perchlorate in water and food require perchlorate-free analytical-grade water.
Millipore developed an ion chromatography method to analyze perchlorate at the ng/L level in high-purity water and assessed the removal efficiency of various combinations of water purification techniques. Because perchlorate was not present in the tap water used to feed the water purification systems, it was added to assess removal efficiencies. A company study showed that reverse osmosis alone removed 97% of the added perchlorate, while ion exchange resins and electrodeionization removed all remaining traces.
Remaining vigilant
It is critical that awareness of these emerging contaminants—and others that will emerge in the future—remain high for both developers of laboratory water purification systems and researchers. New contaminants will certainly be identified and may require novel purification techniques, while concentrations of known contaminants that currently do not pose a concern for most laboratories may rise to levels that have a widespread impact on analyses and experimentation.
The increased sensitivity of analytical methods poses a further challenge. As these methods become more sensitive, the likelihood that existing contaminants may become detectable and interfere with or confound results also increases. These methods—including HPLC, LC-MS, PCR, and microarrays—all share the requirement for one critical reagent: water. Used as blanks for dissolution and dilution of samples, dilution of standards, preparation of mobile phases, and media and buffer preparation, water is central to a laboratory’s productivity and success.
While the presence of trace amounts of emerging contaminants may not currently be an issue in most laboratories, all researchers should be aware of what is in the water they use and how it might impact their studies.
Chromatography
Few factors affect HPLC analyses more than the use of contaminated water for mobile phase. While poor water quality is one of the easiest problems to fix, it is one of the least-understood factors in an analytical laboratory. Between 70% and 80% of HPLC performance issues are ultimately attributed to water quality in eluents, samples, and standards.
A study showed that the purity of the water used for the mobile phase can greatly impact the quality of data obtained from HPLC. A typical reversed-phase HPLC gradient elution requires equilibration of the column with several column volumes of the weak (aqueous) solvent. Organic contaminants in the aqueous solvent may adsorb at the head of the column and cause baseline shifts and the appearance of extraneous peaks, which can interfere with the spectral identification and quantitation of low-level analytes.
In the study, commercially available HPLC-grade bottled water without total oxidizable carbon (TOC) specifications was compared with freshly delivered ultrapure water with a TOC level below 5 ppb. When bottled water was used as a mobile phase in HPLC separations, baseline variability and poor chromatographic performance were observed, as compared to the results observed when ultrapure water was used. It can be assumed that the bottled water contained some organic contaminants that contributed to these poor results.
Genomics
The presence of bacteria or bacterial by-products such as nucleases can also have a significant impact on experiments. When conducting genomics studies, scientists require nuclease-free water to prevent sample degradation and maintain integrity of RNA and DNA. Nucleases in a lab’s water can interfere with experiments employing PCR and other methods that measure or manipulate these nucleic acids.
Gene expression
DNA microarrays are now a ubiquitous tool for measuring the variation or expression levels of thousands of genes in a single experiment. The presence of organic compounds and ions in the water can adversely affect hybridization, and interfere with the detection and measurement of genes using fluorescence.
Proteomics
High-purity water is required in the sample preparation for proteomics analysis to prevent degradation or contamination of the sample. To separate and identify proteins successfully using electrophoresis or chromatography, the use of high-quality water is again paramount. Protein or peptide analyses that use mass spectrometry also require extremely pure reagents to avoid contamination of the ionization chambers and interferences in the mass analysis.
Immunoassays
Bacterial enzymes that mimic the activity of reagents such as alkaline phosphatases can interfere with immunoassays. Endotoxins in a laboratory water supply can disrupt cell growth and function in tissue cultures and cell-based assays.
Cell culture
Endotoxins and heavy metals in a laboratory water supply can disrupt cell growth and function and affect cell-based assays.
Conclusion
Purified water is one of the most commonly utilized reagents in the laboratory. It is used throughout experimental protocols in virtually every type of application. Contaminants present in purified water can therefore have a significant impact on experimental results.
The emergence of new contaminants and our ability to detect existing contaminants in water at extremely low levels present us with a number of important questions that must be continually addressed:
* How might these emerging contaminants impact laboratory analyses?
* At what concentrations will these contaminants be cause for concern?
* Do existing purification technologies effectively remove these contaminants or must new strategies be developed?
Researchers must be certain that their water purification systems effectively remove common and emerging contaminants or run the risk of unexpected results or delays in their experiments.
Estelle Riche, Ph.D., is an Applications Support Scientist at Millipore. Estelle_riche@millipore.com
Maricar Tarun, Ph.D., is an Applications Scientist at Millipore Maricar_tarun@millipore.com
References:
1 Donn J., Mendoza M., Pritchard J. AP probe finds drugs in drinking water. Associated Press (2008)
2 Dove, A. Drugs down the drain. Nature Medicine 12, 376 - 377 (2006)
3 Fono L.J. and MacDonald H.S. Emerging compounds: a concern for water and wastewater utilities. Journal of the American Waterworks Association 100(11):50-57 (November 2008).
4 Colborn, T., Dumanoski, D., and Myers, J.P. Our stolen future: Are we threatening our fertility, intelligence, and survival? A scientific detective story. New York : Dutton, 1996.
5 Riche, E., Ishii, N., and Mabic, S. Generating high-purity water for endocrine disrupter analysis. The Column. pp 14-21 (July 2006)
6 Castillo, E., Riche, E., Kano, I., and Mabic, S. Trace analysis of perchlorate: Analytical method and removal efficiency of purification technologies. The Peak pp 21-29 (2008).
7 Mabic S., Regnault C., Krol J. The misunderstood laboratory solvent: reagent water for HPLC. LCGC North America 23(1):74-82 (2005).
8 Tarun, M., Monferran, C., Devaux, C., Mabic, S. Improving chromatographic performance by using freshly delivered ultrapure water in the mobile phase. LC/GC: The Peak pp 7-14. (June 2009).
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