Benomyl Residues in Selected New Zealand Foods - A report for the Ministry of Healthate of publication: June 2000
Benomyl is used worldwide on a variety of foods to protect them from fungal decay during their growing period and post-harvest. It is one of a family of benzimidazole fungicides which include thiophanate methyl (TM), carbendazim (methyl benzimidazole-2-yl carbamate or MBC) and thiabendazole (TBZ).
The fungitoxic principle of benomyl and TM is actually MBC. It is also the decomposition product of benomyl and thiophanate methyl. As MBC is stable and benomyl and TM are not, any analyses usually involve converting all residual benomyl or TM to MBC, and analysing for MBC alone. As a consequence of this, regulatory limits for benomyl or TM or MBC on food are usually all expressed solely as MBC.
In July 1998, the New Zealand Food Amendment Regulations 1998 were passed and the broad food categories of fruits, vegetables and cereals were deleted from the second table of regulation 257 for benomyl, carbendazim and thiophanate methyl. These were replaced by new maximum residue limits (MRLs) for more specific foods such as avocados, berries and other small fruits (grapes), beans, cereal grains, citrus fruits, cucurbits (like cucumber), lettuce, pome fruit and tomatoes. The new MRLs were established to more accurately reflect modern Good Agricultural Practice (GAP) for this group of fungicides.
In anticipation of these changes, the Ministry of Health considered it important to gain some knowledge of baseline benomyl levels in selected foods in the New Zealand food supply. These data could then be used as a basis from which further work could ascertain the impact of the 1998 regulatory amendment on the incidence of subsequent benomyl residues on food.
Reserve food samples from the 1997/98 New Zealand Total Diet Survey (NZTDS) were used as the main source of samples for this project because its sampling was initiated in 1997 and completed by June 1998, just prior to the 1998 regulatory amendment involving benomyl. The four regions sampled in the NZTDS were Auckland, Napier, Christchurch and Dunedin. Avocados, strawberries and rock melons, which were not sampled in the NZTDS, were purchased in Christchurch in March and June 1999.
Methodology was established and validated so that all samples in the survey could be analysed for both benomyl (as MBC) and the other benzimidazole fungicide, thiabendazole (TBZ). In addition, by interpreting data in terms of the simulated typical diets of the population groups used in the 1997/98 NZTDS, dietary exposures of benomyl (as MBC) and TBZ could also be estimated.
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