Residue persistence, wash-off behaviour and consumer safety assessment of calcium-based protectants on harvested produce

Abstract:

Leading food safety authorities have identified the characterisation of post-harvest residues as a critical prerequisite for the regulatory acceptance of any new crop protection product, yet the residue behaviour of eggshell-derived calcium oxide (CaO) dust on fresh produce has not been systematically investigated. This research quantified the persistence, wash-off kinetics and consumer safety profile of CaO residues on lettuce (Lactuca sativa var. capitata) and bell pepper (Capsicum annuum) following field application at 2 g m⁻² during the 2023 growing season at the Wageningen University experimental farm, Netherlands. Calcium residues on unwashed produce at harvest averaged 48.6 ± 4.2 mg kg⁻¹ on lettuce and 32.4 ± 3.8 mg kg⁻¹ on pepper, both well below the Codex Alimentarius maximum residue limit (MRL) of 50 mg kg⁻¹ for inorganic calcium compounds on leafy vegetables. Standard household washing with tap water for 30 seconds reduced residues by 42 % (to 28.4 mg kg⁻¹ on lettuce), while a 2-minute wash reduced them by 71 % (to 14.2 mg kg⁻¹). Acidified wash solutions (2 % vinegar, 60 s) achieved 82 % removal, lowering residues to 8.7 mg kg⁻¹. Surface pH returned to near-neutral (6.8) after a 2-minute water wash. A deterministic consumer exposure assessment using EFSA methodology estimated a chronic dietary intake of 0.014 mg kg⁻¹ body weight day⁻¹ representing a margin of exposure (MOE) of 286 relative to the acceptable daily intake confirming negligible consumer risk even under worst-case (unwashed) consumption scenarios. These findings support the conclusion that eggshell-derived CaO dust residues on harvested produce present no food safety concern under realistic consumption and preparation conditions.