Restricted Use Pesticide Usage: West Kauaʻi
Waimea to Mānā
Executive Summary (2020-2021)
Our analysis of restricted use pesticide (RUP) usage data in the West Kauaʻi includes the communities of: Waimea, Kekaha and the Mānā Plain.
West Kauaʻi is home to the most frequent application of restricted use pesticides (RUPs) in Hawaiʻi. Chronic exposure is linked to a series of health and environmental impacts, even at low levels. Children and families on Kauaʻi live, recreate and attend school near parcels with some of the highest pesticide use on the island. Analysis of reported pesticide applications for 2020 and 2021 shows extremely large uses of highly hazardous chemicals, including fumigants, persistent herbicides, and neurotoxic insecticides. Many of these substances are known to drift, contaminate water, are toxic to aquatic species and cause serious short- and long-term health impacts, particularly for children.
2020 & 2021
Key Findings
1. Most Frequent Application of RUP’s in Hawaiʻi
RUPʻs were applied the most frequently in West Kauaʻi (between Waimea and Mānā). Chronic exposure is linked to a series of health and environmental impacts, even at low levels. Frequent usage occurs on Mānā Plain adjacent to Polihale State Park.
2020: RUPʻs were applied 4.6 times per day on average
2021: RUPʻs were applied 3.8 times per day on average
2. Usage Near Coastal Areas Threatens Aquatic Life
Heavy usage occurs directly adjacent to coastal areas. Pesticide run-off from plantation era ditches on the Mānā Plain run through agrochemical fields and drain directly out into the ocean.
From 2019-2021 between 13 to 16 active ingredients/RUPʻs were used in West Kauaʻi, all are considered toxic to aquatic species.
3. Massive Fumigant Use Near Schools
Sulfuryl Fluoride dominated fumigant applications in 2020 (~3,888 lbs).
Aluminum Phosphide, although smaller in mass (8 lbs), is an extremely deadly fumigant gas.
These fumigants are volatile, neurotoxic, and associated with respiratory and central nervous system impacts.
Off-site movement via air makes proximity to schools and residential areas particularly concerning.
4. Persistent Herbicides Threaten Water and Ecosystems
S-Metolachlor (964 lbs in 2020; 1,273 lbs in 2021) is persistent, mobile in soils, and a probable carcinogen. It also poses significant aquatic toxicity risks.
Atrazine (2,802 lbs in 2020; 311 lbs in 2021) is an endocrine disruptor, affecting amphibian development, and contaminates both groundwater and surface water.
Bicyclopyrone saw a dramatic increase in 2021 (335 lbs → 1,920 lbs). It poses ecological risks to aquatic life even at moderate exposures.
5. Widespread Use of Highly Toxic Insecticides & Herbicides
Methomyl (434 lbs in 2020; 219 lbs in 2021) is a highly toxic carbamate that inhibits cholinesterase, causing neurodevelopmental risk, particularly for children.
Permethrin, Zeta-Cypermethrin, Beta-Cyfluthrin, Esfenvalerate, and Cyfluthrin (several hundred lbs across both years) are synthetic pyrethroids highly toxic to bees, fish, and aquatic invertebrates.
Chlorantraniliprole (58 lbs in 2021) has lower mammalian toxicity but still poses risks to certain non-target arthropods.
Paraquat dichloride (890 lbs in 2020; 20 lbs in 2021) remains an acutely toxic herbicide with potential for fatal exposure even at very low quantities.
6. Communities Face Complex Chemical Mixtures
Multiple high-hazard chemicals—including fumigants, neurotoxic insecticides, herbicides, and pyrethroids—were applied concurrently in the same landscapes.
Combined exposure amplifies risks for:
Neurodevelopmental harm in children
Immune and endocrine disruption
Long-term chronic disease
Regulatory systems typically evaluate chemicals individually and do not fully account for mixture or cumulative exposures near schools.
Schools At Risk
Pesticide residues travel miles from application sites into schoolyards, homes, water catchments, and air. Chronic exposure threatens children’s developing bodies, contributing to:
Brain development impacts
Respiratory harm and asthma risk
Childhood cancer susceptibility
Hormonal/endocrine interference
Schools within 1 mile of RUP applications (2020–2021):
Ke Kula Niihau O Kekaha LPCS, Kekaha
Kekaha Elementary, Kekaha
Kula Aupuni Niihau PCS, Kekaha
St. Theresa School, Kekaha
Waimea Canyon Middle, Waimea
Waimea High, Waimea
Year-to-Year Trends
2020: Highest frequency of RUP applications in Hawaiʻi. Extremely large applications of fumigants (Sulfuryl Fluoride, Aluminum Phosphide) and persistent herbicides (Atrazine, S-Metolachlor) dominate. Methomyl and pyrethroids create acute toxicity risks for children and pollinators. All RUP’s applied are toxic to aquatic species and applied close to marine environments.
2021: Highest frequency of RUP applications in Hawaiʻi. Fumigant use decreased, but S-Metolachlor and Bicyclopyrone increased significantly. Insecticide use remained substantial, with continued presence of permethrin, pyrethroids, and Methomyl. Paraquat application dropped but still presents acute exposure hazards. All RUP’s applied are toxic to aquatic species and applied close to marine environments.
Overall hazard remains high, driven by large-mass herbicide use and ongoing applications of neurotoxic insecticides and pyrethroids.
If you want the full West Kauaʻi Report, email safefarmssafefood@gmail.com 