Persistence, dissipation, and risk assessment of a combination formulation of trifloxystrobin and tebuconazole fungicides in/on tomato

Multi-locational supervised field trials were conducted in different agro-climatic regions in India to study dissipation of trifloxystrobin and tebuconazole in tomato after spraying a combination formulation (tri-floxystrobin 25% + tebuconazole 50%, 75WG) at recommended doses: (i) single (trifloxystrobin 87.5 g a.i. ha(-1) + tebuconazole 175 g a.i. ha(-1)) and (ii) double (trifloxystrobin 175 g a.i. ha(-1) + tebuconazole 350 g a.i. ha(-1)). Fruit samples were extracted with ethyl acetate using a modified QuEChERS method. The residues (parent fungicides + metabolite) were analyzed and confirmed by GC-ECD and GC-MS, respectively. The half-life (t(1/2)) of trifloxystrobin and tebuconazole in tomato varied from 1.08 to 1.72 and 1.13 -to 1.64 days at single; and 1.27 to 2.13 and 1.24 to 1.96 days at double dose, respectively. Since maximum residue limit (MRL) at pre-harvest interval (PHI) of 5 days is impractical, as tomato is usually harvested and consumed almost everyday after the last spray, the risk assessment was performed at minimum PHI of 1 day. Accordingly, on the basis of supervised field trial data and using OECD MRL calculator, MRL of 0.5 and 1.5 mg kg(-1) at single dose were proposed for trifloxystrobin and tebuconazole in/on tomato, respectively.