Pesticides do not simply disappear once they are banned or withdrawn; many persist in the environment for years, accumulating in soil, water, air, and living organisms. These persistent chemicals, including organochlorines and other synthetic compounds, move through food chains via bioaccumulation and biomagnification, posing long-term risks to human health, wildlife, and ecosystems. Evidence from studies in Kenya and across Africa shows that even years after exposure, pesticide residues remain in people, animals, and the environment, highlighting the urgent need for remediation, monitoring, and sustainable pest management practices
It is easy to assume that once pesticides are banned, withdrawn, or no longer applied, the problem goes away. Evidence shows the opposite. Some compounds persist for years or even decades, especially organochlorines and certain newer synthetic chemicals that resist degradation. This means that even after a pesticide is banned or withdrawn, there is still a need to address the effects it has already left behind in human bodies, animals, and ecosystems.
Pesticide residues in human and animal bodies
A recent NTV documentary featured a pathologist who studies pesticide residues, especially paraquat, in people. The pathologist found that even farmers who had not worked on their farms for three or four years still had traces of pesticides in their bodies. This is not a new discovery. Other studies have also found pesticide residues in animals, showing that these chemicals can stay in the body for a long time, not just after short-term exposure.
Some pesticides break down quickly, but others, called Persistent Organic Pollutants (POPs), can stay in the body or environment for many years. One reason is bioaccumulation, in which small amounts accumulate in body tissues over time. These residues can also move up the food chain. For example, when pesticides enter water, fish can absorb them, and then larger animals, including people, eat the fish. As the residues move up the food chain, their levels can increase. This is called biomagnification.
Biomagnification can also occur during breastfeeding, where a lactating mother passes pesticide residue to her infant through breast milk. Toxicologists describe breastfeeding children as being at the top of the food chain because their exposure comprises what the mother has already accumulated through her diet and environment. Young children are particularly vulnerable because their body systems are still developing, and their small body weight increases their exposure and the effects. A systematic review of 49 studies focusing on Latin American women reported a 100 per cent prevalence of pesticide contamination in breast milk, with DDT (Dichlorodiphenyltrichloroethane) and its isomers being the most commonly detected compounds.
Pesticide residues in water, soils, and air
Pesticides persist extensively in soils. According to recent studies, approximately 80-90 per cent of sprayed pesticides persist in soils for extended periods. Because they can interfere with soil microbial populations and disrupt nutrient cycling, pesticide residues are a major contributor to soil deterioration and declining soil fertility.
Pesticides are also found in the air, in solid, liquid, or gaseous forms. The atmosphere plays a significant role in pesticide movement through processes such as aerial spraying, wind erosion, volatilisation from soils and crops, and emissions during production. From the air, pesticides can enter the human body through inhalation or skin contact.
During a Symposium organised by the Route to Food and partners in Kisumu, scientists reported persistent pesticide residues in water, soil,At a symposium in Kisumu organized by Route to Food and partners, scientists reported finding persistent pesticide residues in water, soil, and animals like snails in farming areas. Their studies showed that African soils are widely contaminated, especially with insecticides, and that many sites contained multiple chemicals, including some not allowed in the European Union. This contamination poses risks to soil life and ecosystem health, and it shows that pesticides can cross borders.
Research presented by Faith Kandie, a lecturer and water quality researcher Moi University, focused on a case study of pesticide pollution in the Lake Victoria South Basin in Kenya, which found that 26 parent compounds and five transformation products of pesticides and biocides were detected in water samples. Even more telling were the sediment and “biota” – the living organisms like sails - which held high concentrations of atrazine and DEET, even when the water itself seemed clear. Sediment analysis identified 55 pesticides, with concentrations reaching up to 110 ng/g organic carbon. Some compounds, such as thiacloprid, were not detected in water but were present in both biota and sediments. Contamination patterns varied by land use, with rice and sugarcane areas showing substantially higher pesticide burdens than maize and tea-growing regions.
From Uganda, Bernard Bwambale, a Public Health Nutritionist at the Global Consumer Centre Uganda, presented a study on pesticide residues in water sources across four regions. The study looked at 86 community water sources, including boreholes, springs, wells, lakes, streams, and taps. They found that 94.2 per cent of these water sources had at least one pesticide residue. Twelve pesticides were found in all regions, with glyphosate, dichlorvos, and chlorpyrifos having the highest average levels. Of the top five pesticides detected, three- aldicarb, dichlorvos, and chlorfenvinphos- are considered highly hazardous. Profenofos was found in most sites, followed by atrazine and chlorpyrifos.
Dr Vera Silva of Wageningen University, through the Soil4Africa project, reviewed existing literature on pesticide contamination in African soils, identifying 88 studies across 25 countries. Only 56 of the 272 soil samples reviewed, about 21 per cent, were pesticide-free, indicating widespread contamination. While water samples were dominated by fungicides, soil samples were primarily contaminated with insecticides, reflecting their greater persistence in soil.
On the other hand, Dr Mary Gikungu, a Natural Scientist and the Director at the National Museums of Kenya, highlighted the impacts of synthetic pesticide use on natural heritage. In birds, organochlorines and organophosphates cause high toxicity, leading to mortality, reproductive failure, and behavioural disruptions. Mammals exposed to contaminated vegetation, water, or prey experience poisoning, reduced fertility, and weakened immunity, with wildlife poisoning incidents increasingly reported near agricultural landscapes. Broad-spectrum insecticides also kill beneficial insects, particularly pollinators such as bees, undermining pollination services and destabilising ecosystems. In aquatic systems, pesticide runoff into rivers and wetlands causes fish, amphibian, and invertebrate deaths, reproductive impairments, and disruptions of aquatic food webs.
Addressing persistent pesticides through policy and practice
Thus, there is a need to address persistent residues that are already present in the environment and in living organisms. This includes active remediation of contaminated soils and water, long-term biomonitoring of residues in people and animals, and sustained surveillance of environmental impacts. According to the Food and Agriculture Organisation, bioremediation is a cost-effective and promising approach to restoring contaminated soils. It involves using biological agents, such as plants, bacteria, and fungi, to naturally degrade pollutants by metabolising contaminants in the environment.
Addressing pesticide persistence also requires supporting farmers to transition away from pesticide-dependent systems altogether. Cultural methods that reduce pest pressure can significantly lower pesticide use. Safer biocontrol options and biopesticides should be encouraged as the first line of external inputs for pest management. Where synthetic pesticides are still required, non-highly hazardous pesticides should be the norm and used only as a last resort.
Lastly, persistence should be a vital consideration during pesticide registration, assessment and withdrawal by national regulatory agencies. Pesticide residues outlive policy decisions.