*Pesticides: Chemistry, Manufacturing, Regulation, Usage and Impacts on Population in Kenya DOI: http://dx.doi.org/10.5772/intechopen.105826*

of the grains annually from approximately 107,000 acres of cultivated land; which highlighted the toxicities of pesticides used and their impacts on human and the environment. The first study was done in 2018 involved prioritization of the pesticide active ingredients by ranking them according to the Q*uantity index* (quantity used) (QI), the Toxicity Potential (TP) and Toxicodynamic Potential (TDP) with regard to *carcinogenicity, mutagenicity, teratogenicity and endocrine disruption*, as described in Dabrowski et al. [99] and Gunier et al. [101], as well as hazard potential (HP), the groundwater ubiquity score (GUS), surface water mobility index (SWMI) to indicate their environmental hazards [99, 100, 102, 103]; and intrinsic toxic potential (ITP) for bioavailability, environmental persistence and bioaccumulation. The **Table 4** shows the criteria for scoring of toxicity potential for specific pesticides, in which a ranking of highest value (8) was given in cases where there was definitive toxic effect


#### **Table 4.**

*Levels of pesticides (kg a.i.) used in Trans Nzoia, their Intrinsic Toxicity Potential (ITP), Hazard Potential (HP), Weighted Hazard Potential (WHP) and Mobility.*

and zero was awarded to endpoints where there was no evidence of toxic effect, and the toxicity potential (TP) was obtained by adding the scores attributed to each of the five toxic effects (carcinogenicity, endocrine disrupter potential, mutagenicity, teratogenicity and neurotoxicity, respectively) for each active ingredient [101].

The GUS index was applied in a logarithmic scale where those pesticides with a GUS index below 1.8 had lower leaching potential while those with a GUS index higher than 2.8 were classified to have high leaching potential [99]. The potential of a pesticide to contaminate surface water resources was determined from surface water mobility index (SWMI), with pesticides having a SWMI tending towards 1 (one) having higher potential to be carried by surface run-off (**Table 4**) [99]. The criteria for scoring human and wildlife (bees and fish) toxicity potential and environmental impacts reported here are discussed in detail by Odira et al. [56] and Otieno et al. [55], respectively.

From this study, a total of 25 pesticides/active ingredients (**Table 4**) were considered significant in terms of their impacts on the environment and human health. The results showed that *glyphosate, mancozeb, terbuthylazine, metalaxyl-M + mancozeb, paraquat dichloride and carbendazim,* were among the most commonly used active ingredients with far-reaching environmental and health impacts. Although there were some pesticides that were not heavily used (e.g. diazinon), they still had significant toxicity from the evaluation scores and, therefore, presented substantial risk to human and environmental health in the area (**Table 4**). It was observed that the fungicide combination *metalaxy-M and mancozeb* was the most commonly used pesticide in Trans Nzoia County accounting for about 19% of all the active ingredients used (**Table 4**), while *diazinon* was the least used pesticide (0.4%) in the county. Trans Nzoia is generally damp and cold most times of the year, a condition that promotes occurrence of fungal diseases which perhaps explains the heavy usage of metalaxyl+mancozeb fungicide combination in the county. The amounts of herbicides such as *glyphosate, terbuthylazine, paraquat, metolachlor and atrazines*, were also high as expected, because of large farm sizes (5–30 acres) (**Table 4**). In addition, *topramezone + dicamba, 2,4 D-Amine, S-Metolachlor, atrazine, cymoxanil + propineb, diazinon, carbendazim, tebuconazole, glyphosphate and deltamethrin* were prioritized as active ingredients with higher potential to contaminate surface and groundwater, in the area. *Glyphosate, mancozeb, S-Metolachlor, terbuthylazine tebuconazole, paraquat dichloride and topramezone + dicamba* presented enormous risk according the weighted hazard potential (WHP) evaluation, but had low potential to contaminate surface water and groundwater due to their low GUS index, and as a result, they could present minimal risk to aquatic organisms and human through consumption of drinking water. Pesticides with high Koc (as well as high water solubility and low soil halflives) (data not presented here) have low potential to contaminate water resources and, therefore, present minimal risk to humans. *Thiamethoxam* with low WHP (**Table 4**), had very high GUS index (ranking of 4) and very high SWMI score (4), and also had the highest potential to contaminate the environment and highest potential toxicity scores (4) to birds, mammals, aquatic invertebrates and bees, respectively. Whereas there were also pesticides with high potential to present risks to humans and the environment due to the high WHP, like the top 5 in **Table 4**, including *glyphosate etc,* such risks may not be via water because of their low mobility. The environmental exposure potentials (EEP), and non-target toxicity data of commonly used pesticides in the area were compiled (full data not included here).

In a similar study done in 2019 in the same county, involving different farmers a full range of pesticides (45 a.i.'s in all) was used over 1 year (full data not shown), including

#### *Pesticides: Chemistry, Manufacturing, Regulation, Usage and Impacts on Population in Kenya DOI: http://dx.doi.org/10.5772/intechopen.105826*

their physical-chemical properties and toxicity indices were reported. The toxicity indices, i.e. TP, EEP, GUS, and SWMI, were used to evaluate potential toxicity to humans and the environment. Most of the farmers (99.4%) involved in the survey applied pesticides, consisting of 10 different fungicides in various formulations, 5 OP's, 5 neonicotinoids, 6 pyrethroids, 2 carbamate insecticides, 4 herbicides, heptachlor (which is banned) and Abamectin, respectively; and most of them falling in the WHO Class I and II. The used pesticides in that year included *carbendazim* (32.9%), *epoxiconazole* (17.6%), *diazinon* (20.4%), *imidacloprid* (23.6%), *metolachlo*r (28.2%), *amitraz* (56.3%), *chlorpyrifos* (10.6%) and *acetochlor* (9.1%), with smaller amounts of *cypermethrin* (5.5%) and *heptachlor* (1.2%). The most applied pesticide class was the OPs (34.8%). It was found that 18.4% of the pesticides applied in the study area were persistent in soil sub-systems, 31.6% were persistent in water, and 10.5% and 13.2% had the potential of contaminating ground and surface water resources, respectively [55, 56]. The ranked order of human toxicity potential associated with the used pesticides in the area in 2019 was *teratogenicity (31.6%), neurotoxicity (29.0%), endocrine disruption (7.9%), carcinogenicity (7.9%), mutagenicity (2.6%) and multiple toxicity potentials (10.5%)*. In addition, 18.4% of the used pesticides, including *acetamiprid, heptachlor, amitraz, chlorimuron ethyl, azoxystrobin, lufenuron and copper oxychloride*, had higher potential for bioconcentration in the living tissues, while most of the pesticides, (39.5%) and (18.8%), respectively, were highly toxic to aquatic invertebrates and earthworms. All the pesticides applied in the study area in 2019 were potentially harmful to human health, if not properly handled. Round up which is restricted in the EU, as well as carbofuran, carbosulfan and heptachlor, which are restricted and banned, respectively, in Kenya, were also used.

In horticultural farming, where farms are often smaller (1–2 acres), the amounts of insecticides and fungicides used are often higher in comparison to the amounts of herbicides [4, 90]. In a survey done in 2015 and 2016 in Meru in Central Kenya, which is famous for horticultural farming of fruits and vegetables for local consumption in major cities such as Nairobi and for export, respectively, high quantities of insecticides such as *deltamethrin, dimethoate, chlorpyrifos, carbaryl, methoxychlor, λ-cyhalothrin, endosulfan sulfate, cypermethrin, zeta-cypermethrin, malathion, diazinon and propoxur*, and even the banned pesticides including *parathion, carbofuran, heptachlor, dieldrin and endrin*, were used over the 2 year period, compared with only smaller quantities of only two herbicides, *glyphosate and paraquat*, and one fungicide a.i., *mancozeb* [4]. Fungicides such as *carbendazim* and several *neonicotinoids* were also reported in French beans, tomatoes and kales, bought during harvesting on the farms, confirming their usage on the farms [4, 104]. The farmers (26%) reported health effects after using pesticides, with most effects (>12 respondents out of 173) experienced when *dimethoate, malathion, heptachlor, endrin, dursban (chlorpyrifos), parathion and dieldrin*, were used. Nine (9) of the pesticides used in Meru county, including *parathion, methomyl, endosulfan, endrin, dieldrin, methoxychlor, heptachlor epoxide, carbofuran and endosulfan sulfate* were very toxic (WHO class I), 12 were toxic (WHO class II) and 5 were moderately toxic (WHO class III) [4].

In Muranga in Central Kenya, where small-scale farming of avocados, tea and coffee are the main cash crops, and maize, beans and bananas are the main food crops, various categories of pesticides, including neonicotinoids, acaricides, fungicides, insecticides and herbicides, were found to be used in 2021 [90], although the quantities of these products were not reported. Using honey bee pollen as an indicator of used pesticides in county, eleven (11) pesticides were confirmed to be present in the honey, including *carbendazim, carbofuran, Spinosyn A, spinosyn D, acetamiprid, chlorpyrifos, thiamethoxam, imidacloprid, acephate, trifloxystrobin and indoxacarb* [90].

A national survey done in 2020 covering 32 counties located in all agricultural regions in Kenya established that mostly subsistence farming is practiced in the counties, and the major pests affecting crops were insects and rodents, where farmers used various synthetic pesticides (80%) as well as home products (68%), with 84% of the most common pests being caterpillar-related pests such as *stalk borers, white flies, worms, army worms and cut worms, aphids, termites, weevils, rodents and fungi*. A large variety of pesticides, including mainly pyrethroids, organophosphates (*e.g. diazinon, dimethoate, pirimiphos methyl, chlorpyrifos*), fungicides (*metalaxyl-M+ mancozeb*), carbamates (*carbaryl*), neonicotinoids (*thiomethoxam*), IGRs (*pyriproxyfen*), rodenticides (*zinc phosphide*) and unspecified herbicides, were used [105]. Some of the homemade products included *lemon grass, aloe vera, ashes, cloves, marigold extracts, pepper, salt and solanum apple*; for example, *ashes and chillies* were used to control insects such as *aphids in vegetables* [105]. The large variety of pesticides used by farmers, in this study, corroborates those pesticides used in regions such as Trans Nzoia, Muranga and Meru counties [4, 55, 56], and similar types of pests reported here have also been reported and discussed extensively in a government and other reports [106, 107]. The need for pesticides sometimes is absolute because frequent unexpected attacks by pests sometimes occur, for example in 2017, 40% of farms were reported to be infested with the fall armyworm [108].

Other researchers have also reported on pesticide use and impacts in other regions of the country, including vegetable farming districts of Kiambu, Kirinyaga, Nyandarua, Muranga, Meru and Makueni [109, 110], where mostly WHO Class I and II pesticides were used and acute poisoning cases were reported; Lake Victoria basin including Nyando, Kericho and Nandi districts [54], where tea, coffee, sugarcane, maize and vegetables were cultivated, and in which 14 different active ingredients were used against maize stock borer (86% of farmers), aphids (70%), cutworms (60%), diamond black moth (50%), thrips (28%), termites (20%) and weeds (4%), and 4 of the active ingredients were known to be highly toxic to bees and birds [54]. Herbicides were used in tea, coffee and sugarcane and insecticides and fungicides, respectively, largely on vegetables [54], with frequent cases of misuse, including application of banned OCs, and declines in pollinating insects and Red-billed Oxpecker bird species being reported [54]. Mburu et al. [111] found that 141 different pesticides were used in 20 horticultural farms along the small Lake Naivasha shore catchment alone, six of them (4.3%) belonging to WHO Class I, including carbamates (*oxamyl and methomyl*), *bipyridylium, strobilurin, tetranortriterpenoids, azole* and OPs (*fenamiphos*), and 20 of them (14.3%) in the WHO Class II. The farmers also used 4 species of natural predators (*Trichoderma spp*, *Paecilomyces spp*, *phytoseiulus persimilis spp* and *Amblyseius spp*), and entomopathogenic fungi, which are registered by PCPB, as biopesticides [111]. Some of the impacts of pesticides on Lake Naivasha water have been highlighted and residues of carbamates and organophosphates have been detected in the water [92, 95]. However, much less work on pesticides and their impacts than expected in global terms is being done in Sub-Saharan Africa [112].

Recently, however, some impacts on pesticide policy in Kenya have started being felt [43]. The route for food initiative (RTFI) (an NGO) in 2019 conducted a study and found that 77% of the 230 ingredients registered in Kenya have been at least withdrawn from the EU market or are heavily restricted due to their chronic human toxicity and environmental effects (based on fish and bees), and additional 19 of them are not listed in the EU database [43]. The RTFI report further highlighted the carcinogenic, mutagenic, endocrine disruptive, neurotoxic and male infertility effects of most of them [43]. Following these concerns, the Kenya Organic Agriculture

*Pesticides: Chemistry, Manufacturing, Regulation, Usage and Impacts on Population in Kenya DOI: http://dx.doi.org/10.5772/intechopen.105826*

Network (KOAN) in collaboration with Eco-Trac Consulting did a survey in 2020 and produced a comprehensive report giving detailed accounts of pesticide usage and impacts in Kirinyaga and Muranga counties in Central Kenya, where intensive horticulture is practiced for subsistence and export purposes [84]. The aim of the study was to provide the evidence needed to advocate and promote a transition from harmful pesticides, to safer alternatives such as GAPs and bio-pesticides [84]. The risk assessment was done according to the EU protocols. Apart from the information on toxicity of 64 active ingredients and 142 formulations being used to control 30 insect pests, 24 weeds and 11 plant diseases, respectively, in the two counties, they also highlighted issues such as misinformation, misuse, mishandling of pesticides and lack of education

and awareness as some of the main challenges the two counties faced [84]; a good example being *methamidophos,* which was not registered for use by the PCPB and likewise, no product containing *acephate* was registered for use on tomatoes, but these two pesticides were being used by farmers, illegally and incorrectly, resulting in residues of *acephate* and *methamidophos*, which are both very toxic [113, 114] exceeding the MRLs set by KEBS and EU in some samples of tomatoes [84]. They concluded that many of the pesticides used in Kenya are highly toxic, belonging to WHO Class I and II, and have already been banned or heavily restricted in other countries such as China, India and Europe, where most of them are imported from Kenya [43, 84]; and their risks need to be assessed with the aim of withdrawal or banning.

An Expert Taskforce [115], in 2021, was appointed by the NGOs to conduct an evaluation of selected pesticide active ingredients (from the PCPB database), including 20 insecticides, 5 fungicides and 4 herbicides, respectively, which are widely used in agriculture in Kenya [115]. The toxicity scores were obtained according to the methods of Dabrowski et al. [99]. Based on their evaluation, they recommended that seventeen (17) of the active ingredients should be withdrawn immediately, five (5) should go through phased withdrawal and only three (3), *clodinatop, flubendiamide and flufenoxuron*, should be retained [115]. The NGOs used the report and successfully pushed for a 'Pesticide Bill' to be introduced in parliament in 2020 aiming at the withdrawal/banning of pesticides considered harmful, from the Kenyan market. The PCPB is currently in the process of conducting a regulatory review of a priority list of highly active ingredients from the PCPB database, including those recommended by the expert taskforce, in support of the bill [115].

#### **4.2 Pesticide use in malaria vector control in Kenya**

Malaria remains the major cause of morbidity and mortality globally with 219 million cases reported in 2017, resulting in 435,000 estimated deaths, 61% of them being children under the age of 5 years [116–118]. The integrated malaria vector management program recommended by the WHO outlines a multipronged approach involving five methods, which include, (i) spraying with recommended insecticides against adult mosquitoes in their habitats, (ii) using insecticide-treated mosquito nets (ITNs), (iii) indoor residual spraying (IRS), whenever necessary, (iv) larval source management, and (v) early diagnosis and treatment; but only ITNs, IRS and early diagnosis and treatment, are implemented in Kenya. It is believed that lack of implementation of sustained larval control has reduced the positive gains made in combating malaria in Kenya, and it still remains a major killer accounting for 10,500 deaths annually [7].

Malaria vector control using long-lasting insecticidal nets (LLIN), has gradually increased in Western Kenya from the year 2000 [7], with about 11 million LLINs distributed freely by 2011; still far from reaching the universal coverage of all vulnerable populations. In these LLIN interventions, *permethrin*-treated LLIN has been used in various endemic zones such as Bondo, Teso, Rachuonyo and Nyando [119]. Pyrethroids such as *fenitrothion, lambda-cyhalothrin and alpha-cypermethrin*, and DDT have been used in IRS. However, with the resistance of the mosquito vectors to pyrethroids widely reported, spraying with *pirimiphos-methyl* on walls in Migori county in Nyanza [7] has been done. Although use of biopesticides such as entomopathogenic fungi has not been embraced, several small-scale trials with biolarvicides such as *B. thuringiensis israelensis (Bti)* and *Bacillus sphaericus (B.s)* in form of water-dispersible granules have reported positive results against various species of mosquito larvae along Lake Victoria shores [7]. The low residual activity makes larval control using the two interventions costly since repeated applications of the bacterial strains to the breeding sites would be necessary, and suitable formulations such as slow-release methods have to be considered. Biorational pesticides such as *Wolbachia*, *Metarhizium anisopliae, methoprene*, *hydropene, p*yriproxyfen*, B. thuringiensis and Spinosad*, which have very low human toxicity and are biodegradable, have not been significantly adopted for larval and adult mosquito control in Kenya [7].

### **5. Conclusions**

The chemistry, manufacturing, importation and regulatory processes regarding pesticides in Kenya as well as their usage and impacts on humans and the environment have been discussed. All the various categories of pesticides, i.e. organochlorine, organophosphate, carbamate, pyrethroid and neonicotinoid insecticides, as well as fungicides, herbicides and biopesticides, which are used in the country, have been considered. Important information on a total of 1447 formulations and 157 active ingredients, respectively, for use in agriculture and public health sectors, are listed on the Pest Control Products Board database and is available freely to the public. A significant number of biopesticides are manufactured in the country and are used in horticulture. A number of studies have been conducted in major agricultural regions, which have characterized pesticides, their toxicities, types of crops and pests, usage and human and environmental health risk indices, since the 2000, but the reports have not made any impact on pesticide regulation, and very toxic active ingredients belonging to the WHO Class I and II, some of them already banned or removed from the EU, seem to dominate the market in Kenya. However, recent pressure from NGOs made an impact on government and parliament and a bill was introduced in 2020, aiming at more strict enforcement and banning of some of the very toxic pesticides, which have already been banned in the EU market. The PCPB which is the government institution charged with the responsibility of regulating pesticides in the country is currently reviewing some of the products, which can be replaced by safer alternatives, for banning.

## **Acknowledgements**

The authors wish to thank the National Research Fund of Kenya (NRF) for their support under the Multidisciplinary Research Grants.

*Pesticides: Chemistry, Manufacturing, Regulation, Usage and Impacts on Population in Kenya DOI: http://dx.doi.org/10.5772/intechopen.105826*
