Could Toxic Chemicals from The Florida FWC’s Aquatic Vegetation Spray Program Be Accumulating in the Fish We Eat?

The Florida Fish and Wildlife Commission (FWC) sprayed nearly 900,000 pounds of herbicide active ingredients on Florida waters in 2017 to kill invasive plants. This raises the question, how much of these chemicals are we ingesting when we eat fish from these waters? The EPA recently conducted a large-scale study of the chemicals present in the fillets of freshwater fish species (USEPA 2009). Surprisingly, of the 268 chemicals examined, none of the top four chemicals used by the FWC were analyzed, which includes glyphosate, endothall, 2,4-D, and diquat.

A further point of concern is that most herbicides are mixed with surfactants that increase the toxicity and pervasiveness of the entire herbicide formulation compared to the active ingredient alone. Research on the surfactants used with glyphosate-based herbicides for land-based applications has shown that many surfactants are laden with toxic heavy metals such as arsenic, chromium, nickel, lead, and cobalt that greatly exceed safe drinking water standards (Defarge et al. 2018). Of the toxic metals found in surfactants, only arsenic was tested by the EPA in fish (with few tests of Florida fish). Do aquatic-based surfactants contain these heavy metals as well? Unfortunately, this question remains untested.

Even if surfactants don’t, many land-based herbicides used in agriculture and industry enter bodies of water during times of significant rainfall and can accumulate to potentially hazardous levels. The city of Okeechobee derives its drinking water from Lake Okeechobee. Okeechobee’s drinking water test results from the EPA and the Florida Department of Environmental Protection show that while levels of arsenic, lead, and chromium fall within legal limits, they are several times higher than state and national averages, and up to 100 times higher than the health guidelines set by state or federal health agencies designed to minimize cancer risk. Studies have found that lead and arsenic in particular can bioaccumulate in fish to higher levels that exceed safety standards in other parts of the world, such as the lower Nitra River in Slovakia (Andreji et al. 2006), yet are not tested by our governmental regulatory agencies.

Returning to herbicides, the manufacturers claim that their products don’t bioaccumulate in fish. However, Wang et al.’s study from 1994 shows that glyphosate and 2,4-D concentrated in fish to levels up to 40 times that of the surrounding water in an enclosed tank experiment. Peak concentrations were found a few days after the initial exposure, and the herbicide concentrations in the tanks approximated that of an FWC spraying operation (if not lower). The peak concentrations of chemicals in fish would make them rank among the most glyphosate and 2,4-D laden foods tested. One question not addressed in the study is how much herbicide accumulated specifically in the edible portions of the fish such as the muscles, rather than organs not usually consumed. Studies examining glyphosate levels in chickens (Shehata et al. 2014) and cattle (Krüger et al. 2014) raised on a conventional, glyphosate-rich diet found that glyphosate does accumulate in muscle and fat. A rat study showed that the concentration of glyphosate in bones was nearly one hundred times higher than in muscle or fat. This suggests that certain preparations of fish such as fish stock or stews could potentially release a much higher concentration of chemicals than a fillet and should especially be avoided when consuming fish from suspect locations.

A final consideration is that the chemicals regularly used by the FWC are most likely present at additional amounts in Florida waters from agricultural uses. While the herbicides from a single spraying event may dilute and break down fairly quickly in an experimental setting, the situation is more complex in real-life bodies of water. It’s possible that a frequent aquatic spray schedule and/or agricultural sources of herbicides prevent fish from truly “detoxing.” Plus, many herbicides bind to sprayed vegetation and suspended particles in the water, both of which eventually settle to the bottom to form sediment where herbicides can persist over long time-frames. Strong storms can stir up the bottom and re-suspend chemicals back in the water column. The South Florida Water Management District’s DBHYDRO database for Lake Okeechobee shows very limited water and sediment tests for the top four herbicides used by the FWC in the past 15-20 years, but confirms the presence of 2,4-D in water and sediment from at least one popular recreational location, S191 (Nubbins Slough).

These studies point to the need of more thorough tests of Florida fish for additional toxic heavy metals and herbicides, particularly in areas and at times that maximize herbicide concentrations in the water, including during extensive aquatic vegetation spraying operations, times of heavy rainfall, or after strong storms. Otherwise, what we are ingesting will remain a potentially disturbing mystery.


How much glyphosate and 2,4-D were in the fish studied by Wang et al. 1994 and how do these amounts compare to the acceptable daily intake of these chemicals?

Acceptable Daily Intake (ADI) of Glyphosate set by health authorities:

USA: 1.75 mg/kg body weight (formerly 0.1 mg/kg in the 1980s before industry pressure)

Europe: 0.5 mg/kg body weight (formerly 0.3 mg/kg before industry pressure)

HOWEVER: recent studies have shown negative effects of consuming glyphosate at levels equal to lower than 1.75 mg/kg, so these guidelines are meaningless (review in van Bruggen et al. 2018; see also

1 kg =2.2 lbs

average person is about 80 kg

ADI for glyphosate would be:

mg/kg x 80 kg = 8 mg

mg/kg x 80 kg = 24 mg

mg/kg x 80 kg = 40 mg

1.75 mg/kg x 80 kg = 70 mg

A 4 oz serving of fish – 113 g – .113 kg

Tilapia had 1.3 ppm glyphosate = 1.3 mg/1 kg in 0.05 ppm of glyphosate

SFWMD publication mentioned 0.5 ppm glyphosate in a one meter mix zone (or 0.16 ppm in 3 m zone), so ppm in Tilapia could be as high as 3.9 ppm

1.3 mg/kg x .113 mg = .147 mg

Foods with highest concentrations of glyphosate residues:

2.837 ppm Quaker Oatmeal Squares Breakfast Cereal (Environmental Working Group data)

1.3 ppm Tilapia exposed to glyphosate at 0.05 ppm in water in Wang et al. experiment

0.930 ppm Quaker Old Fashioned Oats (Environmental Working Group data)

0.564 ppm Soy Sauce (maximum value found by Rubio et al. 2014)

0.0311 ppm Coors Light (U.S. PIRG data)

0.0144 ppm Florida Natural Orange Juice (Environmental Working Group data)

Acceptable Daily Intake (ADI) of 2,4-D set by health authorities:

WHO (World Health Organization): 0.01 mg/kg

ADI for 2,4-D for 80kg person would be: 0.01 mg/kg x 80 kg = 0.8 mg

A 4 oz serving of fish – 113 g – .113 kg

Carp had 20 ppm = 20 mg/1 kg in water with 0.5 ppm of 2,4-D

20 mg/kg x .113 mg = 2.26 mg….that’s almost 3x ADI


Andreji, Jaroslav & Stránai, Ivan & Massányi, Peter & Valent, Miroslav. (2006) Accumulation of Some Metals in Muscles of Five Fish Species from Lower Nitra River. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering. 41. 2607-22. 10.1080/10934520600928003.

Defarge, N., Vendômois, J.S., & Séralini, G.E. (2018) Toxicity of formulants and heavy metals in glyphosate-based herbicides and other pesticides. Toxicology Reports. 5. 156-163.

Krüger M, Schledorn P, Schrödl W, Hoppe HW, Lutz W, et al. (2014) Detection of Glyphosate Residues in Animals and Humans. J Environ Anal Toxicol 4: 210. Doi: 10.4172/2161-0525.1000210

Rubio F, Guo E, Kamp L (2014) Survey of Glyphosate Residues in Honey, Corn and Soy Products. J Environ Anal Toxicol 5: 249. Doi: 10.4172/2161-0525.1000249

Samsel, Anthony & Seneff, Stephanie. (2015) Glyphosate, pathways to modern diseases IV: cancer and related pathologies. Journal of Biological Physics and Chemistry. 15. 121-159. 10.4024/11SA15R.jbpc.15.03.

Shehata, Awad & Schrödl, Wieland & Schledorn, Philipp & Krueger, Monika. (2014) Distribution of Glyphosate in Chicken Organs and its Reduction by Humic Acid Supplementation. The Journal of Poultry Science. 10.2141/jpsa.0130169.

U.S. Environmental Protection Agency (USEPA). 2009. The National Study of Chemical Residues in Lake Fish Tissue. EPA-823-R-09-006. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

van Bruggen, Ariena & MM, He & Shin, Keumchul & V, Mai & Jeong, K.C. & Finckh, Maria & J.G., Jr, Morris. (2018) Environmental and health effects of the herbicide glyphosate. Science of The Total Environment. 616-617. 255-268. 10.1016/j.scitotenv.2017.10.309.

Wang, Y -S, Jaw, C -G, Chen, Y -L. (1994) Accumulation of 2,4-D and Glyphosate in Fish and Water Hyacinth. Water, Air and Soil Pollution. 74: 397-403.