A Kenyan study has raised concerns about the chemicals used to ripen and preserve fruits after laboratory tests found that approximately 95 per cent of samples examined in February 2025 exceeded acceptable chemical limits.
The findings, which cover bananas, tomatoes and mangoes sold in Nairobi, Meru, Murang’a and Kirinyaga, point to significant variations in chemical contamination across different months, with bananas emerging as the most affected fruit.
Researchers Nicholas Mwenda Jacob, Lily Masinde and Palmer Imbenzi examined 392 fruit samples collected from farms, open-air markets and supermarkets over eight months, between September 2024 and April 2025.
Their study, published in the International Journal of Professional Practice in 2026, found that approximately 26 per cent of all samples contained contaminants above the acceptable thresholds used in the investigation.
However, the monthly findings revealed a particularly sharp increase in January and February 2025.
The proportion of samples exceeding acceptable limits rose to approximately 67 per cent in January before climbing to 95 per cent in February.
“February 2025 was the peak month for contamination pressure,” the researchers state.
The average total chemical level also reached approximately 260 parts per million (ppm) during February, the highest recorded level in the investigation.
The findings contrast sharply with September and November 2024, when the proportion of samples exceeding acceptable limits was approximately zero per cent.
Although the levels declined after February, the study found that chemical concentrations remained relatively elevated, with the average total chemical level standing at approximately 173 ppm in April 2025.
Among the three fruits examined, bananas recorded the highest proportion of samples exceeding acceptable chemical limits.
Approximately 40 per cent of banana samples exceeded the relevant thresholds, compared with about 20 per cent of mangoes and 17 per cent of tomatoes.
The researchers attributed the differences partly to the application of chemicals intended to modify or accelerate fruit ripening.
Bananas and mangoes are climacteric fruits, meaning they continue to ripen after harvesting, making ripening management an important part of their handling and distribution.
The laboratory analysis also identified specific substances that raised concerns.
The study reported a mean acetylene concentration of 1.38 mg/kg in carbide-treated fruits, above the 0.7 mg/kg reference threshold used in its analysis.
Arsenic residues were also detected in eight per cent of mango samples, prompting the researchers to raise concerns about potential toxicological exposure.
Calcium carbide was the most frequently reported chemical agent, accounting for 42 per cent of reported chemical use, followed by ethephon at 27 per cent.
These findings highlight the need for closer scrutiny of the substances used to ripen and preserve fruits before they reach consumers.
The researchers also identified differences in chemical use across the four counties, with Nairobi recording the highest proportion of surveyed respondents reporting the use of chemical ripening or delaying agents.
Approximately 72 per cent of respondents in Nairobi reported using such chemicals, compared with 68 per cent in Murang’a, 61 per cent in Kirinyaga and 51 per cent in Meru.
These figures represent reported practices among surveyed respondents, rather than the proportion of fruit samples found to contain excessive chemical residues.
When the researchers compared average total chemical concentrations, Murang’a recorded the highest level at 163.95 ppm.
Nairobi followed at 153.21 ppm, while Kirinyaga recorded 146.1 ppm. Meru had the lowest average concentration at 109.67 ppm.
The researchers associated these differences with commercial activity, market demand, supply-chain pressures and logistical challenges.
In Nairobi, the relatively high reported use of chemical agents was linked to intense market demand, rapid produce turnover and pressure to maintain fruit quality.
The findings suggest that the challenges facing farmers and traders extend beyond the chemicals themselves to the economic and logistical conditions under which fruits are handled and distributed.
The study further examined why farmers and traders rely on chemical interventions to preserve produce and maintain its market value.
Its regression analysis identified rainfall variability as the strongest positive predictor of chemical use, with a coefficient of 0.41.
Market pressure followed with a coefficient of 0.36.
The researchers argued that unpredictable rainfall, changing temperatures and postharvest losses increase the pressure to preserve produce and minimise financial losses.
Inadequate cold storage, inefficient transportation systems and limited access to safer postharvest technologies were also identified as contributing factors.
The study explains that “climate variability and market pressure jointly drive chemical use in postharvest systems”.
Calcium carbide emerged as the principal contributor to potential exposure risk in the researchers’ public health model, recording a coefficient of 0.67.
By contrast, stronger regulatory enforcement was associated with reduced risk, recording a negative coefficient of 0.45.
The findings point to the importance of stronger institutional oversight, better training and affordable alternatives to potentially unsafe chemical practices.
The detection of chemical residues above acceptable limits raises questions about the safety of fruits entering Kenya’s markets and the effectiveness of existing food safety surveillance systems.
The potential health implications depend on the chemical involved, its concentration, the amount consumed and the duration of exposure.
The detection of arsenic in some mango samples is particularly concerning because arsenic exposure can pose significant health risks, depending on its chemical form and level of exposure.
Similarly, the reported findings on calcium carbide and acetylene highlight the importance of investigating the substances and practices used in fruit ripening.
However, the study does not establish that consumers who ate the tested fruits developed health complications. Nor does it demonstrate that all bananas, tomatoes and mangoes sold in the four counties were unsafe.
Importantly, the February finding should not be interpreted as evidence that 95 per cent of all fruits sold in Kenya exceeded acceptable chemical limits.
It represents the proportion of samples exceeding the relevant thresholds during that particular month within the study’s sampling exercise.
The researchers have called for coordinated action involving the Kenya Bureau of Standards (KEBS), the Pest Control Products Board (PCPB), the National Environment Management Authority (NEMA), county governments and public health departments.
Among their recommendations is the introduction of mobile residue-testing laboratories capable of screening fruits in high-risk markets.
They have also proposed stronger inspections, training and certification for farmers and traders, alongside improved traceability systems to strengthen accountability throughout the fruit supply chain.
Investment in affordable storage infrastructure, including solar-powered cold rooms and evaporative cooling facilities, is another proposed intervention.
The researchers argue that reducing postharvest losses would ease the financial pressure encouraging farmers and traders to rely on potentially hazardous chemical interventions.
The findings highlight the intersection of climate variability, agricultural supply-chain pressures and food safety in Kenya.
They also raise an important question for regulators: whether existing monitoring systems are sufficiently equipped to identify unsafe chemical practices before affected produce reaches consumers.
For consumers, the study underscores the importance of stronger food safety controls and more transparent monitoring of the fruits entering the market.
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