Carbendazim and metalaxyl residues in post-harvest treated apples

Bramley apples were treated with Ridomil mbc 60 WP, containing carbendazim and metalaxyl, at half and full rate application at 10 and 20 degrees C, and with diphenylamine to control disease during storage. Carbendazim and metalaxyl residues were determined by HPLC and GC/MS, respectively, in apple core, flesh and peel at the initial time, 3 and 6 months after storage under controlled atmosphere conditions of 4.5 degrees C, 5% CO(2) and 1% O(2). The concentration of carbendazim residues in apple flesh was </=0.43 mg kg(-1) in all treatments; the mean concentrations in apple core and peel were 2.2 +/- 1.1 and 5.2 +/- 2.2 mg kg(-1), respectively. The MRL for carbendazim in apple was 2.0 mg kg(-1). The concentration of metalaxyl residues in apple flesh was </=0.22 mg kg(-1); the mean concentrations in apple core and peel were 0.41 +/- 0.18 and 0.79 +/- 0.94 mg kg(-1), respectively. The MRL for metalaxyl in apple was 1.0 mg kg(-1). The temperature of the fungicide solution had little effect on the carbendazim residues but did have some effect on metalaxyl residues. Carbendazim residue content per apple was decreased when diphenylamine was included. A change in the ratio of carbendazim to metalaxyl was noted in the flesh, core and peel of the stored apple. The ratio of carbendazim to metalaxyl was 5:1 in the fungicide mix as applied. The ratio remained fairly constant in the core during storage. However, the ratio changed significantly in the peel and, to a lesser extent, and in a different direction, in the flesh. In the peel, the ratio was around 15:1 at 3 months of storage and 12:1 after 6 months of storage, whereas for flesh the ratios were 2:1 and 4:1, respectively.