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Why diazinon in Africa? — Expanded analysis with most current references (2020–2025)

Executive summary 

Diazinon is an organophosphate insecticide still used in many African agricultural systems because it is effective, inexpensive and widely distributed. However, a growing body of recent studies from Africa (including farm-gate residue surveys in Kenya and regional monitoring studies) plus shifting regulatory actions in high-income jurisdictions (EU non-approval, U.S. product cancellations) and continuing toxicology findings strengthen the case for risk reduction and managed phase-down in high-exposure uses (particularly fresh leafy vegetables and home/domestic uses). Policymakers should combine immediate exposure-reduction measures, sentinel surveillance, and a funded multi-year transition to IPM and lower-toxicity options. PLOS+2Federal Register+2

1. New evidence since 2020 (what’s changed)

  1. Field residue studies in East Africa (2024–2025): Multiple recent studies document detectable — and in some cases high — diazinon residues in leafy vegetables (kale/Brassica) at farm-gate and market levels in Kenya and neighbouring settings, and report gaps in adherence to pre-harvest intervals (PHIs) and GAP. These findings increase the plausibility of dietary exposure for consumers and indicate on-farm misuse or knowledge gaps. MedRxiv+1

  2. Wider residue and environmental detection: Pan-regional residue surveys and soil/water monitoring work (2023–2025) show organophosphate detection in agricultural soils and surface waters in multiple regions; diazinon appears among frequently detected OPs in some studies, which raises concerns for non-target and aquatic species. ScienceDirect+1

  3. Regulatory shifts: The EU removed approval for several OPs and does not approve diazinon for agricultural uses (with the EU review process and MRL monitoring tightening enforcement for non-approved substances). In the U.S., registrants requested cancellations for many diazinon products and the EPA issued cancellation orders (2023), effectively eliminating several key uses. Meanwhile, the Rotterdam Convention continues to process notifications and decisions relevant to hazardous pesticides — COP and CRC activity in 2024–2025 has kept pesticide listing and SHPF (severely hazardous pesticide formulation) proposals in active international discussion. These global regulatory signals affect trade, donor policy and supplier behaviour. EFSA Journal+2Federal Register+2

  4. Toxicology and risk assessment updates: Authoritative agencies (ATSDR, EPA materials and peer-reviewed PBK/TD modelling work) continue to underscore diazinon’s acute cholinergic toxicity and note population variability in sensitivity (children and pregnant women being notable concerns). Newer modelling and toxicodynamic work (2024–2025) improves understanding of within-population variability and supports tighter exposure margins for vulnerable groups. CDC+1

2. Implications of the new evidence for African policy

  • Food safety & exports: Recent farm-gate residue data (Kenya) mean governments must consider sentinel residue monitoring on high-risk crops (green leafy vegetables, brassicas), because international buyers and regional markets will enforce MRLs and rejections have economic consequences. PLOS+1

  • Occupational health: Documented on-farm misuse and informal supply chains indicate elevated acute poisoning risk among farmworkers and family labor; immediate PPE and training interventions are cost-effective first responses. PLOS+1

  • Environmental risk: Detection of diazinon and other OPs in soils and waters increases the urgency for stewardship measures (buffer strips, application timing, runoff controls). ScienceDirect

  • Regulatory coordination: EU, U.S. and multilateral regulatory moves materially change the policy environment and justify regional harmonisation of registration and MRL policies to avoid trade shocks and “export to lower-regulation markets” dynamics. EFSA Journal+1

3. Updated, prioritized policy recommendations (detailed & practical)

Immediate (0–12 months)

  1. Sentinel residue monitoring: Fund a rapid sentinel program for 6–12 months for leafy greens and brassicas at selected markets and farm-gate sites; publish results transparently. (Rationale: recent Kenya studies show on-farm residues.) PLOS

  2. Targeted use restrictions & advisories: Temporarily restrict diazinon use on high-risk food crops (fresh leafy vegetables) pending risk assessment or re-registration decisions. Use time-limited emergency orders if needed. (Rationale: protect consumers and meet trade buyer expectations.) PLOS+1

  3. Rapid training push for agro-dealers/farmworkers: Deploy short courses and pictographic handling/PPE leaflets in local languages focused on PHIs, mixing, disposal, and emergency response. National Pesticide Information Center

Short-to-medium term (1–3 years)

  1. Re-registration and risk re-evaluation: Require registrants to submit current exposure, residue decline, and modern toxicology data for diazinon — suspend high-exposure uses where margins are unacceptable. ATSDR

  2. Subsidised pilot rollouts for IPM/biopesticides: Fund demonstration plots and seed grants so smallholders can trial alternatives (pheromone traps, biopesticides, cultural controls). Link subsidies to training and monitoring. PMC

Medium-to-long term (3–7 years)

  1. Phase-down pathway: Develop a multi-year schedule to phase down diazinon for food-crop uses where safer alternatives exist; pair each phase with technical and financial support. (Rationale: avoid livelihood shocks.) PAN Europe

  2. Regional harmonization of MRLs & registration: Work through regional economic communities to align MRLs, registration criteria, and import notifications so intra-regional trade is protected and regulatory arbitrage is minimised. pic.int

Cross-cutting

  1. Clinical surveillance & poison control capacity: Strengthen sentinel clinical reporting (standard case definitions, rapid reporting to ministry of health) and ensure dependable antidote/management supplies where OP use persists. CDC

4. Research & data gaps (priorities for funding)

  1. Dietary exposure assessment for typical consumption patterns of leafy vegetables across age groups in affected countries.

  2. Residue decline (PHI) field trials under smallholder management regimes for crops where diazinon is used.

  3. Effectiveness and cost–benefit of candidate IPM/biopesticide substitutes in local conditions.

  4. Occupational exposure monitoring (cholinesterase testing) among spray operators and family labor in hotspots.
    These address direct uncertainties impeding regulatory decisions and will better tailor local policy.

5. Most current references (selected, high-impact — 2020–2025)

I prioritized primary studies, official regulatory documents and authoritative toxicology sources. Below are the citations + quick note on why each is important. Click the links to view the source (links are to the documents returned by the searches I ran).

  1. Oromo GO, Owuor PO, et al. (2025). Diazinon residues levels in farm-gate Brassica oleracea var. acephala of Kimira-Oluch smallholder farm improvement project, Kenya. PLOS ONE / PMC. — Recent farm-gate residue study showing measurable diazinon residues and GAP/PHI gaps. PLOS+1

  2. Oromo GO et al. (2024). Diazinon residues… medRxiv preprint (Sep 2024). — Earlier preprint of the Kenya/region work; useful for methods and preliminary data. MedRxiv+1

  3. PIC Circular LIX & LXI (Rotterdam Convention publications), PIC Secretariat, UNEP/FAO (Jun 2024; Jun 2025). — Official records of notifications, COP/CRC activity and the PIC Circulars (relevant to international listing and trade obligations). pic.int+1

  4. European Food Safety Authority / EU reports (EFSA / EC reporting; EU Regulation updates 2021–2024). — Demonstrates the EU’s regulatory trajectory (non-approval status and MRL enforcement environment). See the EU pesticide residues / regulation notices (e.g., Regulation texts and EFSA annual monitoring reports). 

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