Image by Fellipe Ditadi.
Aquatic plant eradication campaigns of poorly understood need, impacts, and risks have resulted in tens of tons of herbicides containing PFAS active ingredients applied to drinking water sources for millions of people in New York State.
New Yorkers can count among their fortunes both their plentiful waters and the many organizations that protect lakes, rivers, and reservoirs from industrial pollution as well as pesticide and fertilizer runoff, among other stresses. Non-native and/or invasive species and our responses to them also exert complex effects on aquatic ecosystems and drinking water sources. In recent years, concerns about the non-native aquatic plant hydrilla have driven us to costly, extensive, and poorly understood chemical interventions that are likely harmful to the millions of people connected to the impacted waterbodies.
A relatively recent arrival in New York State, hydrilla has a longer history in US regions ranging from Florida to Delaware to California and can thrive in shallow, nutrient-rich environments. Outreach efforts claim it to be “one of the world’s most invasive plants,” capable of dominating ecosystems at the expense of other species, and even of “hijacking the local economy.” These concerns have sometimes motivated massive, costly eradication campaigns, including in New York.
Hydrilla’s actual menace to aquatic habitats is however not so clear. Concerns about the plant’s ability to impede water flow and recreation seem to originate from experiences in warmer environments with long growing seasons, e.g. in Florida, where its ability to grow to depths of about 20 feet enables expansion throughout shallow lakes and ponds. In larger, deeper waterbodies, it grows only at the periphery. Careful studies document no negative impacts of hydrilla on fish, aquatic insects, or water birds. One examination of 27 different Florida lakes finds no significant declines in diversity or abundance of other plant species due to hydrilla. In Virginia’s Chesapeake Bay, hydrilla accompanied and even supported proliferation of native species and is credited with benefitting the broader ecosystem, similar to other aquatic plants.
After hydrilla was found in 2011 at the inlet and southern end of Cayuga Lake in Ithaca, New York, local and state agencies teamed up to eradicate it. The method of choice has been use of herbicides, predominantly Sonar® H4C, made by SePRO. H4C is a slow-release pellet formulation of the active ingredient fluridone, which comprises 3% of the product. At concentrations of a few parts per billion (ppb), fluridone inhibits the hormone abscisic acid, and thereby photosynthesis, non-selectively harming a broad array of plants. With approval from the NYS Department of Environmental Conservation (NYSDEC) and various local organizations, the Army Corps of Engineers (ACE) has coordinated treatments in regions of the 67 sq. mile lake, which has a maximum depth of over 400 feet, every summer since 2012. According to publicly available reports, applications sum to about 23 tons over five summers between 2019 and 2023, less than half the eradication campaign’s duration.
Though hydrilla has since spread to new shoreline locations of the lake, the program was held up as a success, even serving as a model for a similar effort in the New Croton Reservoir, responsible for about 10% of New York City’s drinking water. Quantities applied here are not publicly available. But permits and project reports provided in response to a Freedom of Information Law (FOIL) request indicate yet more aggressive applications. Though the reservoir spans one twentieth Cayuga Lake’s area and less than one hundredth the volume, over four summers (2021-2024), the NYSDEC authorized the NYC Department of Environmental Protection (DEP) to apply up to 95 tons of Sonar® H4C and Sonar® One (a more concentrated pellet-form product with 5% active ingredient) in total, to target fluridone concentrations of 1-5 ppb. Over 35 tons were applied.
Assessing risks associated with non-native and invasive species, and evidence for both harms and benefits of the often costly interventions taken against them, can be a complex matter. And chemical risks to ecosystems, particularly to drinking water sources, should only be taken in response to grave and pressing threats. Ecological threats posed by hydrilla have often been overstated, and we can find no evidence documenting its harm in deep, cold waterbodies like Cayuga Lake and the New Croton Reservoir. Worse, assessments of the herbicides’ impacts have been sorely lacking. While hydrilla has declined in treatment areas, so have other aquatic plants.
The once thriving native plant populations in Cayuga Lake’s inlet, where hydrilla accounted for only a few percent in 2012, have nearly disappeared after years of repeated treatment. Publicly available monitoring reports suggest significant declines of many species between 2012 and 2019. Some, including the native Elodea, are almost eliminated in areas of the lake where originally abundant. ACE reports after 2019 simply do not report plant abundance, despite noting annual declines for all plants near treatment areas. This should be deeply alarming, as aquatic plants provide food and shelter for many species and help regulate water quality. No monitoring of treatments’ impacts on fish, birds or invertebrates were attempted, despite modern studies finding effects including signatures of endocrine disruption in fish even at low fluridone concentrations. Such harms may be long-lived; though fluridone can persist in sediments over multiple years even in much warmer climes, no monitoring for accumulation or its effects year after year in sediments of the lake or reservoir has been conducted.
Beyond their ecological effects, herbicides applied to drinking water sources constitute a direct threat to human health. The European Drinking Water Directive limits total pesticide concentration from all runoff or unintentional addition to 0.5 ppb, below that intentionally targeted for a single active ingredient in the lake and reservoir. Fluridone is furthermore a PFAS compound according to the definition adopted by the Organization for Economic Cooperation and Development and multiple state laws. Chemicals of this class containing long-lived carbon-fluorine bonds have recently attracted increasing scrutiny for clear harms to human health that were poorly understood in the past. Recent EPA regulations limit concentrations of certain PFAS chemicals in drinking water to a few parts per trillion (ppt), over 100x lower than would have been permissible a decade ago. Intentional fluridone incorporation into food packaging, clothing, carpets, or turf in NYS would be prohibited, but it is nevertheless being deliberately added to drinking water sources for millions of people, at concentrations exceeding limits imposed on other PFAS chemicals by over 100x.
The remaining 95-97% of the pellets is composed of so-called “inert” ingredients. As for all pesticides, these are not publicly disclosed and undergo limited testing for approval, though in many cases can be clearly harmful. While multiple if problematic studies have been published on fluridone’s effects on animal health, despite multiple inquiries to the ACE and the NYSDEC including by local watershed organizations, we have been unable to obtain information as to safety of these “inerts” in drinking water sources, nor their impacts on flora or fauna. Neither fluridone’s decay byproducts nor the fate of the unspecified “inert” ingredients have been monitored. Another summer of applications is being planned as of this writing.
We are troubled by the risks inherent in the application of tens of tons of herbicides to drinking water sources, taken to eradicate a plant whose ecological harms were questionable in the first place, all at a cost of many millions of dollars to taxpayers. Hydrilla and the treatments persist, the collateral damage is unexamined, and the health impacts of these chemicals are unlikely to be salutary. The public is owed a much higher scientific standard for justification and evaluation of any such campaign, if undertaken. Without clearly demonstrated need for herbicide interventions, together with transparent accounting for their profound risks, New Yorkers should demand a firm stop to chemical contamination of ecosystems and critical drinking water sources.
