A variety of unregulated or “emerging” contaminants are being discovered in drinking water and the environment throughout the United States. Although many of these chemicals have been in use since the mid-twentieth century, recent increased detection ability and awareness has confirmed their ubiquitous presence. There is growing public and regulatory concern about exposure to these contaminants, including perfluorinated compounds (PFCs); however, the scientific evidence regarding their health impacts still is not settled. This lack of scientific certainty is delaying regulatory action at the federal and state levels, where regulators are only beginning to address what the public increasingly believes is a major cause of concern. This article details the origin of perfluorinated compounds, the current scientific understanding of their impact, the existing regulatory landscape, and proposed solutions that will provide guidance and certainty for regulators and critical stakeholders, including drinking water suppliers, landowners, and public health advocates.
March 01, 2018
Contaminants of Emerging Concern: A New Frontier for Hazardous Waste and Drinking Water Regulation
Jeff B. Kray and Sarah J. Wightman
PFASs is a generic term for a family of perfluoroalkyl substances, synthetic chemicals that have many useful properties, including fire resistance and oil, stain, grease, and water repellency. See U.S. EPA, Per- and Polyfluoroalkyl Substances (PFASs) under TSCA, www.epa.gov/assessing-and-managing-chemicals-under-tsca/and-polyfluoroalkyl-substances-pfass-under-tsca. The two most widely known PFASs are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). PFASs are found in firefighting foams, wire insulation, cleaners, textiles, apparel, carpet, leather, paper, and paints. See id. Because of their widespread use and persistence (i.e., they degrade very slowly), PFASs are now found worldwide in the environment, wildlife, and humans. See id. According to industry human biomonitoring data, PFOA also is found in the blood of the general population in all geographic regions of the United States. See Perfluorooctanoic Acid (PFOA), Fluorinated Telomers; Request for Comment, 68 Fed. Reg. 18,626, 18,629 (Apr. 16, 2003).
“Emerging contaminants,” or “contaminants of emerging concern,” are previously unknown, unrecognized, unanticipated, unsuspected, or unregulated chemical pollutants. The 1996 Safe Drinking Water Act (SDWA) amendments require that once every five years the U.S. Environmental Protection Agency (EPA) issue a new candidate contaminant list (CCL) to be monitored by public water systems (PWSs). See U.S. EPA, Third Unregulated Contaminant Monitoring Rule, www.epa.gov/dwucmr/third-unregulated-contaminant-monitoring-rule. The third Unregulated Contaminant Monitoring Rule (UCMR 3) published on May 2, 2012, required monitoring for 30 contaminants, including many emerging contaminants, such as PFOS and PFOA. See Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems, 77 Fed. Reg. 26,072 (May 2, 2012).
PFAS chemicals may be harmful to the environment and human health. Because PFASs degrade slowly, they can bioaccumulate in terrestrial food webs and in marine mammals, meaning that organisms higher in the food chain have higher PFAS levels than those lower in the food chain. See e.g., Wash. Dep’t of Ecology, Perfluorinated Compounds in Washington Rivers and Lakes (Aug. 2010) at 33.
Although PFASs are widespread in low concentrations, the main pathways for human exposure include ingestion of contaminated food and water and inhalation of contaminated air. See Wouter A. Gebbink et al., Estimating Human Exposure to PFOS Isomers and PFCA Homologues: The Relative Importance of Direct and Indirect (Precursor) Exposure, 74 Env’t Int’l 160–169 (Jan. 2015). PFAS contamination is of special concern in drinking water. Because PFASs do not easily degrade, they can accumulate in the blood and liver, making consistent exposure to even low concentrations potentially harmful. See EPA, Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA) (May 2016); EPA, Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS) (May 2016). However, despite the research conducted thus far, the science regarding the ultimate health risks of PFAS chemicals is incomplete.
PFAS contamination of drinking water is widespread. An August 2016 study found that PFASs are found in the drinking water for at least 6 million U.S. residents in levels that exceed those in EPA’s health advisory. See Xindi C. Hu, et al., Detection of Poly- and Perfluoroalkyl Substances (PFASs) in U.S. Drinking Water Linked to Industrial Sites, Military Fire Training Areas, and Wastewater Treatment Plants, 3 Envtl. Sci. Tech. Letters 10, 344–350 (Aug. 9, 2016). The two main sources of PFAS contamination in drinking water are manufacturing plants and facilities using aqueous film-forming foam (AFFF) as fire retardant.
Many manufacturing facilities used PFASs starting in the 1950s. In Parkersburg, West Virginia, DuPont used PFOA to make Teflon for over 40 years, resulting in release of PFOA powder into the Ohio River and sludge-containing PFOA into digestion ponds near the facility. PFOA entered the local water table, contaminating drinking water for more than 100,000 people. See Nathaniel Rich, The Lawyer Who Became DuPont’s Worst Nightmare, N.Y. Times Magazine, Jan. 6, 2016, www.nytimes.com/2016/01/10/magazine/the-lawyer-who-became-duponts-worst-nightmare.html. Similarly, in Hoosick Falls, New York, a manufacturing plant used PFOA to make stain-resistant fabric. In a personal injury suit, the plaintiff alleges that employees discharged PFOA by dumping trays of cleaning residue containing PFOA into drains, which contaminated soil, groundwater, and ultimately the town’s public water supply. See Donavan v. Saint-Gobain Performance Plastics, Complaint and Demand for Jury Trial (July 27, 2016). Similar drinking water contamination originating from manufacturing plants has been discovered across the country, including in Minnesota, Alabama, Vermont, New Hampshire, and New Jersey.
PFAS contamination of drinking water is common on and around military installations and civilian airports due to the use of AFFFs used to fight fires. Although recently discovered Department of Defense (DOD) memoranda indicate that DOD knew about the possible risks of PFAS in AFFFs since the early 1980s, DOD only recently began to investigate PFAS contamination on and near its facilities. See Kyle Bagenstose, Records: Military Knew of Foam Dangers in 2001, Bucks County Courier Times, July 15, 2017, www.buckscountycouriertimes.com/8fb1f91c-9848-5d77-89e5-22c80d1fee86.html. In the past several years, the U.S. Air Force alone has identified 200 facilities where there may be PFAS releases, many of which are now undergoing cleanup for contaminated drinking water. See e.g., Air Force Public Affairs, Frequently Asked Questions: PFOS/PFOA (Dec. 1, 2016). The Air Force and Navy have identified at least 24 bases with contaminated drinking water in Alaska, California, Colorado, Delaware, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Virginia, and Washington. See e.g., Bagenstose, Military Knew of Foam Dangers in 2001, supra. The Air Force has spent $150 million for investigation and remediation and is projected to spend millions more to treat water and provide alternate drinking water sources. See Corinne Roels et al., Military Bases’ Contamination Will Affect Water for Generations, Center for Public Integrity, Aug. 18, 2017. For example, a June 2017 Air Force Interim Feasibility Study of Eielson Air Force Base in Alaska developed seven cleanup options to address drinking water wells contaminated with PFAS ranging in cost from $32 million to $67 million.
Despite several decades of manufacturing and use, PFASs are “emerging” in the environmental regulatory context for three key reasons. One, they are now detectable due to improved analytical methods. Two, more data is available, which has resulted in a concurrent increase in academic awareness about the chemicals and their impacts. Three, PFASs have become subject to greater media coverage and public concern.
PFASs are currently classified as emerging contaminants at both the federal and state levels. Both federal and state agencies have determined that PFASs are a known environmental and health risk and have taken a range of steps to begin regulating PFASs; however, regulations across jurisdictions are inconsistent, causing uncertainty for a broad range of water users.
Federal Regulation of Perfluorinated Compounds
In the late 1990s, EPA received information indicating that PFOS was widespread in the blood of the general population and presented concerns for persistence, bioaccumulation, and toxicity. EPA, Per- and Polyfluoroalkyl Substances (PFASs) under TSCA, www.epa.gov/assessing-and-managing-chemicals-under-tsca/and-polyfluoroalkyl-substances-pfass-under-tsca. Following discussions between EPA and 3M—the sole manufacturer of PFOS in the United States and the principal manufacturer in the world—the company terminated production of these chemicals in May 2000. Id. In 2002, EPA acted to limit future manufacture and importation of PFOS and took similar action in 2007 regarding an additional 183 PFASs. See id.; Perfluoroalkyl Sulfonates; Significant New Use Rule, 72 Fed. Reg. 57,222 (Oct. 9, 2007). In addition, EPA’s New Chemicals program reviews alternatives for PFOA and related chemicals before they enter the marketplace to ensure that replacement chemicals do not present an unreasonable risk to health or the environment. EPA, New Chemicals Program Review of Alternatives for PFOA and Related Chemicals, www.epa.gov/assessing-and-managing-chemicals-under-tsca/new-chemicals-program-review-alternatives-pfoa-and (last updated Sept. 14, 2016.)
In May 2016, EPA established drinking water health advisories for PFOA and PFOS, setting the advisory level at 70 parts per trillion. Advisories provide technical information to state agencies and other public health officials on health effects, analytical methodologies, and treatment technologies associated with drinking water contamination; however, complying with such advisories is not mandatory.
EPA has not yet listed any PFASs as hazardous under relevant regulatory schemes, such as the Resource Conservation and Recovery Act (RCRA), Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), Emergency Planning and Community Right-to-Know Act (EPCRA), or Clean Air Act (CAA). Despite EPA’s failure to characterize any PFASs as hazardous, EPA has moved to include at least one PFOA-contaminated site (Hoosick Falls, New York) on the Superfund National Priorities List (NPL). In addition, the U.S. Food and Drug Administration (FDA) has banned three perfluorinated compounds from use in food packaging. Previously, the FDA had allowed the use of these chemicals as oil and water repellents in paper food packaging, but as of January 2016, their use in such applications is prohibited. See Indirect Food Additives: Paper and Paperboard Components, 81 Fed. Reg. 5 (Jan. 4, 2016).
Despite the lack of comprehensive action by EPA and other agencies, members of Congress from districts impacted by PFAS contamination are working through legislative channels to secure funding for drinking water treatment, PFAS cleanup, exposure assessment, and health impact research. On December 12, 2017, President Trump signed the National Defense Authorization Act, which included funding for Navy and Air Force cleanup of polyfluoroalkyl substances and a health impact study of PFOA and PFOS. See, e.g., Senate Amendments 967 and 999 to H.R. 2810, 115th Cong. (2017).
Proposed Solutions and State Regulation Examples
State legislatures and agencies have taken a wide variety of approaches to regulating PFAS chemicals, which provide valuable insights for possible further regulation at both the state and federal level. To provide regulatory certainty and guidance, we propose four solutions: (1) designate PFAS chemicals as hazardous and create cleanup standards; (2) establish binding drinking water standards; (3) regulate the sources of emerging contaminants; and (4) create innovative and novel regulatory solutions.
Designate PFAS chemicals as hazardous and create cleanup standards. Regulating PFASs as hazardous substances and setting cleanup standards at both the federal and state levels would allow water suppliers and users to more easily compel investigations and recover costs incurred while responding to PFAS contamination. Cleanup standards also would give contaminated property owners a benchmark for sufficient cleanup, facilitating source removal of these contaminants and ensuring cleaner drinking water.
Vermont, New Hampshire, Michigan, and Alaska are leading the way in state regulation of PFAS chemicals as hazardous substances, as all four states have established binding cleanup levels for PFOA and PFOS. Vermont has added liquid wastes containing PFOA and/or PFOS in concentrations greater than 20 parts per trillion (0.00002 micrograms (mcg) per liter) to its list of hazardous wastes, VHWMR § 7-211, and has finalized primary groundwater quality standards for PFOA and PFOS at 0.02 mcg per liter, Vermont Groundwater Protection Rule and Strategy, Appendix 1, Table 1. New Hampshire also has an ambient groundwater quality standard of 0.07 parts per billion (0.07 mcg per liter) for combined PFOA and PFOS. Env-Or 603.03(c). The Michigan Department of Environmental Quality set a cleanup standard of 70 parts per trillion (0.07 mcg per liter) for combined PFOA and PFOS in groundwater used for drinking water (see Mich. Dep’t of Envtl. Quality, State Takes Action to Strengthen Environmental Criteria in Response to PFAS Contamination (Jan. 9, 2018), www.michigan.gov/deq/0,4561,7-135—457220—,00.html), and Alaska has set a standard of 0.4 mcg per liter of PFOS and/or PFOA in groundwater and various levels for cleanup of PFOS and PFOA in soil (see 18 AAC 75.341, 345).
Several other states have taken steps toward establishing cleanup levels but have not yet finalized binding standards. In January 2017, Massachusetts released a draft fact sheet titled “Guidance on Sampling and Analysis for PFAS at Disposal Sites Regulated under the Massachusetts Contingency Plan,” which notes that the Massachusetts Department of Environmental Protection considers PFAS chemicals to be hazardous materials under Massachusetts law and that, although no cleanup standard has been set, PFASs must be addressed at cleanup sites where they are possible contaminants of concern. In 2017, the Pennsylvania House of Representatives considered House Bill 1398, which would add perfluorinated chemicals to the commonwealth’s definition of “hazardous substance” in its CERCLA-equivalent cleanup law. The bill also would require the Pennsylvania Department of Environmental Protection to determine whether a chemical should be designated as a hazardous substance within 12 months of the establishment of a maximum contaminant level, health advisory level, or provisional health advisory under the Pennsylvania Safe Drinking Water Act or a similar federal law. As of February 2018, the bill was still under consideration in the Pennsylvania House Committee on Environmental Resources and Energy.
Although New York does not have a binding cleanup standard, effective March 3, 2017, New York regulations list PFOA and PFOS as hazardous substances, require the proper storage of these substances, limit releases to the environment, and enable the state to use its legal authority and funds to investigate and clean up impacted sites. 6 NYCRR Part 597. New York has already used these regulations to issue at least three consent orders relating to the investigation and cleanup of PFOA. See Order on Consent and Administrative Settlement, Index No. CO 4-20160519-01; Order on Consent and Administrative Settlement, Index No. CO 4-20160212-18; Order on Consent and Administrative Settlement, Index No. CO 4-20160415-79.
Finally, since 2016 the Washington State Departments of Ecology and Health have been developing a Chemical Action Plan (CAP) for PFASs. A CAP generally includes analyzing the chemistry, sources, health effects, and environmental data of the chemical at issue, as well as a regulatory and economic analysis coupled with recommendations. See Wash. Dep’t of Ecology and Wash. Dep’t of Health, PBT Initiative Overview (Jan. 7, 2015) at 9. Although the CAP process is important, it does not necessarily result in a substantive rule or policy change establishing a cleanup standard. After the discovery of PFAS contamination in at least three separate public drinking water systems in Washington, the Department of Ecology also is considering whether to formally recognize PFOS and PFOA as hazardous under state law and developing cleanup standards.
Establish binding drinking water standards. Currently EPA only regulates PFAS chemicals in drinking water on an advisory basis, meaning the standards are not binding. This causes confusion for drinking water providers who want to provide safe drinking water to their customers but also need to keep costs reasonable and comply with other relevant regulations. Establishing binding drinking water standards for PFAS chemicals like PFOA and PFOS would clarify the regulatory landscape, giving both drinking water providers and the public greater certainty regarding water safety. Establishing such standards also would increase costs for water providers; however, when coupled with other solutions such as designating PFAS chemicals as hazardous substances, drinking water providers can recover those increased costs from liable parties.
One state, New Jersey, is finalizing binding drinking water standards for two PFAS chemicals. In November 2017, the New Jersey Department of Environmental Protection (DEP) announced it would accept the New Jersey Drinking Water Quality Institute’s recommended drinking water standard of 14 parts per trillion for PFOA. DEP also has formally proposed a standard of 13 parts per trillion for perfluorononanoic acid (PFNA). DEP News Release, Christie Administration Takes Action to Enhance Protection of New Jersey’s Drinking Water, Nov. 1, 2017, www.nj.gov/dep/newsrel/2017/17_0104.htm. Several states have adopted advisory levels similar to EPA’s health advisory limits of 70 parts per trillion. Vermont’s health advisory level for drinking water is 20 parts per trillion; Minnesota has adopted guidance values of 35 parts per trillion for PFOA and 27 parts per trillion for PFOS in drinking water; and Maine has adopted EPA’s health advisory limits wholesale. See Vermont Health and the Environment, Perfluorooctanoic Acid (PFOA) in Drinking Water, www.healthvermont.gov/health-environment/drinking-water/perfluorooctanoic-acid-pfoa; Minnesota Department of Health, News Release: MDH Issues New Guidance on Chemicals in Some Private Wells, City Water in East Metro, Bemidji (May 23, 2017); Maine CDC, Maximum Exposure Guidelines (MEGs) for Drinking Water (Dec. 31, 2016). Connecticut also has established an “action level” for perfluorinated alkyl substances in drinking water, but it is unique in that the level is 0.07 µg/L for the sum of five perfluorinated compounds: PFOS, PFOA, PFNA, PFHxS, and PFHpA. Connecticut Dep’t of Public Health, Action Level List for Private Wells (Feb. 2013). Pennsylvania is considering binding drinking water standards for PFOA, see Jon Hurdle, PA Environmental Regulators to Consider Health Limits for PFOA, NPR: State Impact, Aug. 17, 2017, https://stateimpact.npr.org/pennsylvania/2017/08/17/pa-environmental-regulators-to-consider-health-limits-for-pfoa/; however, as of February 2018, Pennsylvania has not approved a binding standard.
Regulate the sources of emerging contaminants. Although manufacturers of some PFAS chemicals have voluntarily stopped production in the United States, PFAS chemicals are still manufactured overseas, are contained in products in the United States, and, therefore, are still being introduced into our environment. Regulating sources of PFAS chemicals such as firefighting foam, consumer products, and wastewater would limit new sources of contamination and allow regulators to focus on cleaning up legacy contamination.
Several states have acted to reduce the introduction of these chemicals into the environment. In September 2016, California issued a notice of intent to list PFOA and PFOS as known to the state to cause reproductive toxicity under the Safe Drinking Water and Toxic Enforcement Act of 1986 (otherwise known as Proposition 65). California based its decision on EPA’s Drinking Water Health Advisories for the chemicals. On November 10, 2017, both PFOA and PFOS were added to Proposition 65 due to their developmental toxicity. One year after California finalizes the listing of PFOA and PFOS, businesses will be required to provide a “clear and reasonable” warning before knowingly and intentionally exposing anyone to a listed chemical, unless the business can show that the anticipated exposure level will not pose a significant risk of cancer or is significantly below levels observed to cause birth defects or other reproductive harm. CA Health and Safety Code §§ 25249.6, 25249.10. This warning can be given in several ways, including labeling a consumer product, posting signs at a workplace, or publishing notices in a newspaper. See 27 CCR § 25601 et seq. Proposition 65 also prohibits companies that do business within California from knowingly discharging listed chemicals into sources of drinking water. CA Health and Safety Code § 25249.5. Similarly, Washington’s Children’s Safe Products Reporting Rule requires manufacturers to report annually to the Department of Ecology the presence of chemicals of high concern to children (CHCCs) in children’s products offered for sale in Washington. This rule classifies PFOS and PFOA as CHCCs. See WAC 173-334-130; Washington Dep’t of Ecology, Children’s Safe Products Reporting Rule: Chemicals of High Concern to Children Proposed for Addition or Deletion during the 2017 Rule Update (Sept. 2017). In addition, New York prohibited the use firefighting foam containing PFOA or PFOS after April 25, 2017. 6 NYCRR Part 597, and as of February 2018, the Washington legislature is considering House Bill 2793, which would, among other things, prohibit the sale of certain firefighting foams to which PFAS chemicals have been intentionally added in Washington. These state actions indicate a clear trend toward regulation preventing the introduction of PFAS chemicals to the environment, while also moving to regulate the consequences of decades of past use.
Create innovative and novel regulatory solutions. While the basic building blocks of a successful regulatory scheme are described above, regulators also must experiment with new and innovative solutions. Emerging contaminants are pervasive in the modern world and are not limited to PFASs. New chemicals are constantly under development, and regulators rarely discover their negative impacts until years after integration into consumer products and industrial processes and releases to the environment. Innovative regulatory frameworks can anticipate future problems and allow for agencies to quickly address new issues when they emerge instead of only reacting to problems well after they arise.
For example, in January 2017, Michigan’s governor signed Public Act No. 545, which amended Michigan’s Safe Drinking Water Act to require the state or federal government, when it owns or owned real property where a “substance of concern” was used, to provide an alternative water supply to users of a water source impacted by that substance. In addition, the law requires the government to conduct long-term monitoring to delineate the migration of the substance of concern and reimburse a state agency or political subdivision that has provided an alternative water supply to users of an impacted water source. The bill was drafted in response to the PFAS contamination discovered near Wurtsmith Air Force Base, which has caused a fish advisory in the area since 2012 and more than 300 people to find alternative sources of drinking water. See Senate Fiscal Agency, Bill Analysis: Public Act 545 of 2016 (Apr. 3, 2017). The Air Force currently is not complying with its provisions, claiming sovereign immunity, id.; however, the law shows forethought in dealing with cleanup of unforeseen contaminants.
Some states are proactively monitoring for PFAS chemicals. For example, the Minnesota Department of Health is conducting long-term biomonitoring for PFAS chemicals in areas where these chemicals were discovered in the mid-2000s. See Minnesota Department of Health, PFC Biomonitoring: East Metro, www.health.state.mn.us/divs/hpcd/tracking/ biomonitoring/projects/emetro-landing.html (last visited Feb. 8, 2018). The state also is actively investigating sites where PFAS contamination is likely, such as 3M manufacturing and waste disposal facilities, fire training facilities, chrome plating plants, and wastewater treatment plants, and is conducting ambient monitoring to detect PFAS chemicals in the general environment. See Minnesota Department of Health, Perfluorochemicals (PFCs) in Minnesota, www.health.state.mn.us/divs/eh/hazardous/topics/pfcs. In addition, Rhode Island announced it would be testing for PFAS in more than 30 systems across the state, focusing on systems serving less than 10,000 people. Jennifer McDermott, Rhode Island Is Checking Water for Chemical Contamination, Associated Press, Aug. 20, 2017. Similarly, Washington plans to fund up to 500 PFAS samples for known at-risk public drinking water systems, seeking greater distribution of drinking water quality data across the state. Washington Dep’ts of Ecology and Health, PFAS CAP Overview (Aug. 30, 2017). Proactive monitoring can lead to faster problem solving and build trust in regulatory agencies.
Some states also are considering broader chemical management strategies. For example, the Vermont General Assembly considered but failed to pass S.103 last year, which would have established an interagency committee on chemical management tasked with evaluating chemical inventories in Vermont on an annual basis, identifying potential risks to human health and the environment from chemical inventories in the state, and proposing measures or mechanisms to address the identified risks from those chemical inventories. The bill also would have required water quality testing for new groundwater wells used as potable water supplies. These broad chemical management strategies could help identify new contaminants of concern going forward and prevent widespread contamination issues faced with PFAS chemicals.
Finally, some states are attempting to regulate PFAS chemicals in environmental media other than water. For example, New Hampshire considered but failed to pass H.B. 463 in 2017, which would have established air quality standards for devices emitting contaminants that cause or contribute to an exceedance of ambient groundwater quality. Entities with such devices would have had to apply for a permit, pay a fee, and install best available control technology to control the contaminant at issue. This requirement was crafted in response to the PFOA contamination that several New Hampshire public water supplies are facing as a result of PFOA smokestack emissions. See Kimberly Houghton, Lawmakers’ Frustration Aired over Water Contamination Bill, N.H. Union Leader, June 18, 2017, available at http://www.newhampshire.com/environment/Lawmakers-frustration-aired-over-water-contamination-bill-06192017. New Hampshire’s proposed approach recognizes that water contamination can result from larger systematic issues and that regulating chemical content in water alone is not always adequate.
As scientists and regulatory agencies assess potential risks and regulatory strategies, clearly, the issue of how to deal with emerging contaminants such as PFASs is here to stay. Federal and state regulators’ slow progress toward designating PFASs as hazardous, promulgating cleanup and drinking water standards, and regulating the sources of these contaminants has created confusion for water suppliers, landowners, manufacturers, and the public. Until clear and binding regulations are in place, it will remain unnecessarily complex for drinking water suppliers, owners of contaminated land, and others concerned about the potential public health consequences of PFASs to address the sources of PFAS contamination and recover costs from responsible parties. And without regulatory innovation at the federal and state levels, the country will be underprepared for the next wave of emerging contaminants and their unique challenges.