23
Oct
Pesticide Contamination of Seaweed Threatens Public Health, Biodiversity, and Ecosystem Functioning
(Beyond Pesticides, October 23, 2025) A global literature review of pesticide residues in marine seaweed, published in Marine Pollution Bulletin, highlights the widespread presence of pesticides in bioindicator species. As vital coastal primary producers, seaweed acts as a key indicator for regional pesticide contamination patterns. The bioaccumulation within seaweed species also threatens consumers, including humans, as the chemicals can biomagnify as they move through the food web. Pesticide contamination in waterways allows residues to bioaccumulate in seaweed species, presenting risks to public health, biodiversity, and ecosystem functioning.
In addition to the support seaweeds provide for ecosystems, they provide food sources for a multitude of organisms and are of growing socioeconomic importance. “This systematic review identifies, critically evaluates, and synthesizes recent global literature (2015–2024) on pesticide residues detected in seaweeds to delineate contamination patterns,†the authors share. The findings highlight the harmful impacts of petrochemical pesticides on multiple species. Many aquatic species rely on seaweed as a food source, including fish, sea urchins, crabs, snails, brittle stars, and marine mammals such as manatees and sea turtles. Even bacteria and filter feeders consume seaweed when it is decomposed. Birds and land mammals also consume seaweed, including humans who utilize seaweed in various food products due to its high nutritional value.
The literature review incorporates results from twelve studies that assess pesticide residues in multiple seaweed groups, including Chlorophyta (green algae), Rhodophyta (red algae), and Phaeophyceae (brown algae). Overall, despite the most commonly used organochlorine insecticides being banned in many countries, this class of pesticides, with the active ingredients hexachlorocyclohexane (HCH), aldrin, dichlorodiphenyltrichloroethane (DDT), and endosulfan, is the most frequently detected, highlighting the legacy of persistent contamination. Throughout different regions, the pesticide concentrations vary significantly, and the differences noted when comparing algal species can be attributed to the properties of the pesticides and the morphology and lipid content of the algae that can impact bioaccumulation.
Importance of Seaweed
As the researchers state: “Seaweeds constitute a diverse group of photosynthetic organisms that play crucial ecological and socioeconomic roles in coastal ecosystems worldwide. Beyond being fundamental primary producers, seaweeds act as true ecosystem engineers. Their structural complexity creates vital habitats for numerous species of invertebrates and fish.â€
“[C]oastal ecosystems face multiple anthropogenic threats, among which pesticide contamination stands out,†the authors note. They continue: “The intensive and widespread use of pesticides in agriculture, as well as in other human activities, constitutes the main source of these compounds in the environment. The presence of these contaminants in marine ecosystems is a matter of growing scientific concern due to their potential adverse effects on organisms and overall ecosystem health, potentially leading to changes in community structure, loss of biodiversity, and imbalances in ecological interactions.â€
As seaweed species are able to act as effective bioindicators of marine pollution, the detection of pesticide residues highlights the contamination within waterways that impacts multiple nontarget organisms and threatens ecosystem stability. “[T]he bioaccumulation of persistent pesticides in seaweed tissues represents not only a key metric for monitoring ecosystem health but also a potential vector for contaminant transfer into the human food chain, given the growing global market for edible seaweeds,†the researchers state. (See research here and here.)
Literature Review Methodology and Results
In searching for full articles published in English within peer-reviewed journals between the timeframe of January 2015 and December 2024, the authors found twelve articles that met the eligibility criteria and were used to extract twenty data points for the macroalgal groups. This resulted in eight records for Chlorophyta, seven for Rhodophyta, and five for Phaeophyceae. The discrepancy between the twenty data points and twelve studies is due to multiple species being addressed within individual studies.
As the authors point out, there are limitations within this review when comparing studies with differing methodologies and in the low number of total studies that met their criteria. “The scarcity of research addressing pesticide contamination in seaweeds, with only 12 studies spanning a full decade, reveals fundamental gaps that demand strategic intervention,†the authors state. Additionally, they continue by saying: “Perhaps the most significant research gap is the disconnect between contamination quantification and ecological impact assessment. Current studies document the presence and concentrations but rarely establish causal relationships with physiological or ecological effects. Future research should prioritize mechanistic studies examining how pesticide exposure affects seaweed growth, reproduction, biochemical composition, and ecosystem functions.â€
The authors note that the articles included in the review incorporate two studies each that analyze five, four, three, and two distinct species, with four studies examining only a single species. In total, this includes fourteen species of green algae, ten species of red algae, and eight species of brown algae that are contaminated with one or more pesticides.
Notably, out of the twelve studies, seven are focused in India, which the researchers attribute to multiple factors. Since there is a “significant and expanding seaweed cultivation sector, strongly supported by governmental initiatives and investment in research and development,†in India, it is an area with rising concerns over pesticide contamination in coastal zones. The underrepresentation, however, of other areas around the globe in recent research is a limitation within the current literature review.
The analysis of the studies shows a varying number of distinct pesticide types identified within different chemical classes in seaweed samples, with organochlorines representing the most diverse class. Ten different organochlorine pesticide (OCP) residues are identified among all of the seaweed species, highlighting their status as persistent organic pollutants (POPs) that “exhibit exceptional environmental stability, long half-lives, and high lipophilicity, leading to significant bioaccumulation in organisms and biomagnification.†(See studies here, here, and here.)
Within Chlorophyta, current-use pesticides (CUPs), including the pyrethroids bifenthrin and cypermethrin are also detected. Since pyrethroids tend to have lower persistence than POPs in the environment, their presence in seaweed samples shows recent or ongoing contamination in coastal environments.
In Rhodophyta, the concentration of detected pesticides varies significantly. Endosulfan, for example, is prominent in Indian seaweed samples, most likely as a result of its intensive agricultural use in coastal catchments like the Gulf of Mannar. Cypermethrin is also noted in several Indian studies, which “points to more contemporary pollution from its widespread agricultural application and subsequent runoff, given its moderate persistence.†In contrast, a study in Egypt shows higher concentrations of aldrin, HCH, and another organochlorine chlordane, possibly as a result of long-standing contamination from past extensive agricultural use in the Nile Delta and industrial discharges into depositional basins like El-Mex Bay.
Studies of brown algae (Phaeophyceae) “demonstrate a greater overall bioaccumulation capacity for OCPs when compared to green and red algae,†the authors say. “This enhanced capability is likely influenced by their distinct biochemical and morphological characteristics, as well as their interactions with lipophilic compounds present in the environment.â€
The data within all studies, despite differing methodologies and limitations, consistently show how seaweed species bioaccumulate several pesticides, many of which are banned in multiple countries, highlighting the contamination in aquatic ecosystems and adding to the existing body of science on how pesticides threaten health and the environment.
Previous Research
A multitude of studies, referenced in the current literature review and in coverage by Beyond Pesticides, showcase the cascading negative impacts on marine biodiversity and ecosystem functioning that occur with pesticide contamination in coastal ecosystems as a result of agricultural runoff. (See studies here, here, and here, as well as the Daily News archive on water contamination here.)
As highlighted in Daily News, toxic pesticides harm all beings and ecosystems, including coral reefs. Large benthic foraminifera (LBF) are single-celled organisms found on reefs that face adverse metabolic impacts after exposure to the weed killer glyphosate, fungicide tebuconazole, and neonicotinoid insecticide imidacloprid, according to a study published in Marine Pollution Bulletin. The study found that “even the lowest doses of the fungicide and herbicide caused irreparable damage to the foraminifera and their symbionts.â€
Another study, published in the journal Environmental Science and Technology Letters, funded by the National Oceanic and Atmospheric Administration, is the first to find halogenated organic compounds (HOCs) in deep ocean sediment and biota off the coast of California. The test area, known as the Southern California Bight (SCB), is home to historic offshore DDT waste dumping, with part of the SCB designated as a U.S. Environmental Protection Agency (EPA) Superfund site. Forty-nine HOCs were detected in the sediment and biota, many of which are DDT-related and not previously screened for. The presence of these “unmonitored compounds can significantly contribute to the contaminant body burden across a range of marine taxa,†the study states, which leads to impacts on critical food webs and biodiversity. (See Daily News here.)
Additional coverage, in Daily News, entitled Ocean Mammals Genetically Vulnerable to Certain Pesticides, notes how pesticides drain from agricultural fields, poison waterways and coastal areas, and harm wildlife. A study in Science finds that a gene that helps terrestrial mammals break down certain toxic chemicals appears to be faulty in marine mammals — potentially leaving manatees, dolphins, and other warm-blooded aquatic life more sensitive to toxic pesticides, especially organophosphates.
These studies, and more, represent the extensive threats from pesticides to aquatic environments and all of the lives that depend upon them. Learn more from Beyond Pesticides’ Pesticides and You article entitled Pesticides Wreak Havoc on Ecosystems and see additional research on water contamination and impacts on aquatic organisms here and here.
The Organic Solution
Clean water is essential for human health, wildlife, and a balanced environment. Yet, water is being polluted at unprecedented rates, with pesticides, industrial chemicals, nutrients, metals, and other contaminants. To protect water resources, aquatic organisms, and human health, the elimination of petrochemical pesticides and synthetic fertilizers is urgently needed. Removing the sources of agricultural and land management pesticide contamination and adopting organic methods is the holistic solution that benefits both aquatic ecosystem health and overall public health. Â
For more information on the health and environmental benefits of organic, see here and here. Start by buying organic products and growing your own organic food. To make a difference in your community, become a Parks Advocate for the Parks for a Sustainable Future program. For more information, please email our team at [email protected].
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🏞️ Join the webinar next Wednesday! To advance principles of land management that align with nature, Beyond Pesticides is convening the 42nd National Forum, The Pesticide Threat to Environmental Health: Advancing Holistic Solutions Aligned with Nature, bringing together scientists and land managers working to recognize and respect the ecosystems on which life depends. Scheduled to begin on October 29, 2025, 1:00-3:30 pm (Eastern time, US), the virtual Forum is free to all participants. See featured speakers! ➡️ Register here.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Azevedo, G. et al. (2025) Global patterns of pesticide residues in seaweeds: A systematic review, Marine Pollution Bulletin. Available at: https://www.sciencedirect.com/science/article/pii/S0025326X25011841.
