1. Are pesticides a serious problem in U.S. drinking waters?
2. Are there POU and POE systems that can remove them?
What are pesticides?
The legal definition of ‘‘pesticide’’ is: (1) any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest; (2) any substance or mixture of substances intended for use as a plant regulator, defoliant or desiccant; and (3) any nitrogen stabilizer.
Pesticides are called economic poisons. They control undesirable “pests” in our environment so they are intended for beneficial uses. However, because they are poisons to a greater or lesser degree, they are intensively examined and regulated prior to being allowed to be used. There are over a thousand registered pesticide active ingredients and many thousands of registered formulations of combinations of pesticides (active ingredients) and inactive (inert ingredients).
There is a huge database available at http://www.epa.gov/pesticides/PPISdata/. They include antimicrobials and biopesticides, in addition to the conventional substances.
Many pesticides are organic chemicals, but there are also inorganic chemicals like arsenic, lead, chlorate and chlorine that fit the definitions.
There are four major laws that control the uses and human exposures to pesticides in the U.S.: The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), Federal Food Drug and Cosmetic Act (FFDCA) and the Food Quality Protection Act of 1996 (FQPA).
The Safe Drinking Water Act gives the Environmental Protection Agency (EPA) control of contaminants in public drinking water supplies. All pesticides used in the U.S. must be registered (licensed) by the EPA. Registration assures that pesticides will be properly labeled, and that if used in accordance with specifications they will not cause unreasonable harm to health or the environment. Use of each registered pesticide must be consistent with use directions contained on labeling.
FIFRA gives the EPA the authority for comprehensive regulation of all pesticides from their manufacture, transport, sale, distribution and use. Its history goes back to 1910 and it has been amended numerous times.
By law, pesticides must be applied according to the label directions. FFDCA gives the EPA the authority to produce Pesticide Tolerances that set limits on the amounts of pesticide residues allowed in food or animal feed.
FQPA increased the safety standards for assessing new pesticides and also required that older pesticides and tolerances to be periodically reassessed using the new tougher standards. FFDCA and FQPA have special provisions to protect infants and children. The registrants pay the costs of the registration and review processes carried out by the EPA.
Pesticides production and use
According to the Cornell Safety Education Program (CSEP), pesticides production in the U.S. tripled from 400 million pounds in 1950 to over 1.4 billion pounds in 1980 — this probably included exports as well as domestic use. However, remarkably, the estimated use in 2001 was less, 1.25 billion pounds (www.extension.org), indicating more restrictive and cancelled registrations and more careful application management.
The types of pesticides in current use have also changed substantially, from persistent pesticides like DDT and chlordane, to more biodegradable pesticides. About half are herbicides like glyphosate and atrazine. Application rates are very small, ranging from a few ounces to a few pounds per acre.
Pesticides in drinking water
Surface waters and especially small streams in agricultural areas frequently have measurable amounts of at least one pesticide. This can be seasonable, such as from the widespread use of the pre-emergent herbicide atrazine in the Corn Belt in the spring.
Groundwater contamination is a function of soil transmissivity and physical and chemical properties of the pesticides used in the area. Groundwater contamination tends to be persistent once it occurs because of its slow movement and less biochemical transformation that occurs in that environment.
Nitrate increase is a possible indicator of the possibility of some pesticide presence because of its use in fertilizers and solubility and mobility in water. It can also be an indicator of potential microbial contamination.
Among many health and environmental assessments, the registration process uses specific criteria involving the potential for applications and use patterns and quantities to contaminate drinking water, and the potential human exposure that could result in relation to risk-based concentrations.
The EPA establishes Maximum Contaminant Levels for each contaminant based upon toxicology, health risk and control feasibility. In the European Union, pesticides detections in drinking water are a method for regulating their use in the watershed of a water supplier. If any pesticide’s level exceeds 0.1 ppb in the drinking water or the total exceeds 0.5 ppb, the use in the watershed is investigated and modified, up to a ban in that watershed.
Public drinking water suppliers have specified monitoring and reporting requirements. They are required to produce Consumer Confidence Reports that describe the condition and regulatory status of the supply. Compliance information is available online or from the supplier.
Drinking waters are regulated for at least 30 pesticides, plus four disinfectant-related chemicals like chlorite. That count is probably low because numerous other chemicals have minor uses in applications such as fumigants. Most pesticides are seldom detected in compliance monitoring, or do not exceed standards when detected.
CSEP reports that 22 pesticides have been detected in U.S. wells, and up to 80 were estimated to have the potential for movement in groundwater under favorable conditions.
If a source water is contaminated by any regulated chemical, it must be managed to achieve the standard. This could include the use of appropriate water treatment technology or changing the source, such as by drilling a new well.
Drinking water safety
In addition to the regulations, EPA’s Water Office has published Drinking Water Health Advisories (EPA 822-S-12-001) that include about 100 additional health-based values for unregulated contaminants.
EPA’s Pesticides Office has published drinking water benchmark values for more than 355 pesticides. The latter needs to be read carefully because they are not prospective drinking water standards. They calculated benchmarks from health data applying a 20 percent relative source contribution for drinking water. Actually, relative source contributions (RSC) in standards usually can range from 20 to 80 percent — the higher the RSC, the higher potential drinking water standard.
For example, the 20 percent RSC for chlorate yields a benchmark of 210 ppb, but applying an 80 percent RSC, as used by Canada and the World Health Organization, would give a benchmark of 840 ppb.
Where are pesticides in drinking water’s greatest concerns?
Pesticides can be found in some surface waters and groundwaters, however, many pesticides are regulated. Public water supplies are generally monitored and treated, so they are usually not a concern.
The more likely problems would be found in rural home wells, shallow groundwaters, associated with agricultural activities, in porous sandy soils and seasonally where small streams are draining agricultural areas and in small public water systems where limited monitoring is required.
There are probably millions of at risk home wells, and thousands of small public water supplies.
Is POU/POE decentralized water treatment effective for compliance with drinking water standards?
The Safe Drinking Water Act (SDWA) specifically allows use of POU or POE for public water system compliance. When EPA lists compliance technologies for Maximum Contaminant Levels or Treatment Techniques for small systems, they must include packaged or modular systems and POU and POE treatment units.
POU, POE or bottled water may be required as part of a Variance or Exemption delay from meeting a regulation to avoid an unreasonable risk to health during the time that the compliance delay is allowed.
Bottled water is not allowed for compliance. If the American National Standards Institute (ANSI) has issued product standards applicable to a specific type of POU or POE treatment unit, those units must be independently certified to those ANSI standards (see Water Technology, April 2014, Professor POU/POE for details).
Central treatment using packaged plants is available for small water supplies. These are usually more cost effective for small systems than having engineered systems designed on site. They also are usually more rapidly installed, automated and less costly to operate than “stick built” systems. One would suspect that consulting engineers prefer the latter.
Some heavily chlorinated pesticides that bind well to sediments, like DDT or chlordane, are removed by conventional coagulation and sand filtration.
Granular activated carbon technology is usually effective, especially for the more modern pesticides that are less hydrophobic. Ozonation can reduce the less chlorinated more reactive pesticides. Reverse osmosis could also be effective, though probably most costly and wasteful of reject water.
Be sensitive to co-contamination by nitrate and microbials that might indicate potential for pesticide contamination.
Chemical analysis for the broad spectrum of pesticides can be expensive — in the multiple hundreds of dollars per sample. However, it would often be possible to pinpoint the most likely pesticide contaminants from other monitoring data that has been collected in the area, and from information on the pesticides that have been used.
Available pesticides have been shifting to less toxic, less persistent and more biodegradable chemicals, and they are being applied at lesser loadings. Many registered pesticides are applied annually at the billion pound level — many are regulated in drinking water so they are generally managed in public drinking water supplies. Rural groundwaters and small streams probably have the greatest likelihood for unmanaged pesticide water contamination that can be treated by POU and POE technologies.
Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.