Assessment of Veterinary Drugs and Pesticide Residue Levels in Cow and Camel Milk From Kiambu, Laikipia and Isiolo Counties, Kenya

Abstract

Exposure to pesticides and veterinary drugs residues in foods of animal origin is a major public health concern due to increase usage of this chemicals. Humans are exposed to these chemicals through ingestion of contaminated food, skin absorption and inhalation. Among all food sources milk is one of the main sources of chemical contaminants. The current study aimed at evaluating organochlorine and organophosphate pesticides and veterinary drug residues levels in cow and camel milk collected from Kiambu, Isiolo, and Laikipia Counties between 2017 and 2018. Kiambu, Isiolo, and Laikipia Counties are of interest to this study as they are associated with the highest production of cow and camel milk in Kenya, however, little is known of the levels of pesticides and the effect of seasons on the pesticide levels in milk collected from these areas. A total of 82 camel milk and 90 cow milk samples were collected from 8 different wards of Kiambu, Isiolo and Laikipia Counties and a total of 18 organochlorines and 14 organophosphates were evaluated using gas chromatography-tandem mass spectroscopy (GCMS-TQ8040). Eleven veterinary drug residues were evaluated using ultra high-performance liquid chromatography-tandem mass spectroscopy (UHPLC-MS/MS). Variations in the pesticide and veterinary drug levels in milk collected from the different counties was evaluated using Analysis of variance and Tukey’s post hoc test. Differences in the pesticide and veterinary drug levels in milk samples collected in the dry and wet seasons were evaluated using the independent sample student’s t-test. p< 0.05 was considered significant in all cases. With the exception of heptachlor with mean concentration of 12.38 ng/mL for Kiambu, 4.62 ng/mL for Isiolo and 13.42 ng/mL for Laikipia county, all other pesticides in cow and camel milk were below the maximum residue limits. Chlorthiophos-1 had the highest mean concentration of 46.07 ng/mL in cow milk from Kiambu ranging between <0.2 to 387.47 ng/mL while camel milk from Isiolo and Laikipia had mean concentrations of 10.77 ng/mL and 14.30 ng/mL respectively. Multiple residues of veterinary drugs were below the maximum residue limits for sulphonamides of 100 ng/mL. The mean level of tetrachlorvinphos in camel milk was greater during the dry season than the wet season. The mean levels of γ-BHC, o’p-DDD, and cis-nonachlor in camel milk were greater during the wet season than during the dry season. Similarly, the mean levels of dieldrin, o’p-DDD, nonachlor, and endosulphan in cow milk were greater during the wet season than during the dry season. There was no difference in the mean levels of all the veterinary drug tested in camel milk during wet and dry season. However, the mean levels of sulfathiazole in camel milk during wet season was higher than in dry season. The mean levels of veterinary drug residues in cow milk were higher in dry season relative to wet season. Cow and camel milk collected from Isiolo, Kiambu, and Laikipia counties are contaminated with heptachlor which implies that consumers are exposed to the associated risk such as cancer. There is a need for government policy to mitigate the contamination of cow and camel milk in the study area by the organochlorine heptachlor. The season of sample collection appears to have an effect on the mean levels of some pesticides and veterinary drugs but not others. There is a need for studies to unravel the underlying causes of season dependent variations in the mean levels of some pesticides and veterinary drugs.