Assessment of accumulative DPA residues throughout storage and packing facilities

The use of DPA for the control of superficial scald on apples and pears is no longer an option for fruit exported to the EU. This is due to regulations where the acceptable MRL’s were reduced from 10.0 (pears) and 5.0 ppm (apples) to 0.10 ppm.

The aim of this trial was to assess the potential risk of cross-contamination on untreated fruit by analysing DPA residue levels on fruit at the bin, cold store and pack line level.

In the 2013 season, DPA contamination was monitored at flume, bin and cold store level. Flume water, floor and wall swabs, and untreated fruit in cold rooms previously used for DPA treated fruit storage were analysed for DPA residue.

In the 2013 to 2016 seasons, DPA residue levels were monitored over ±5 months on untreated fruit in rooms that previously stored DPA treated fruit and in rooms that had not stored DPA treated fruit previously.

In the 2016 season untreated fruit were subjected to a 2000 ppm DPA dip and send to three laboratories as part of a ring test

2013

Untreated fruit stored with DPA treated fruit had residue levels higher than 0.1 ppm after only 4 weeks of storage. There was no contamination from old and new plastic bins and new wooden bins. Only after 14 weeks cold storage levels of 0.05 ppm were detected on fruit stored in old wooden bins. Low to no residue levels was detected in flume water. Untreated fruit in cold rooms that stored DPA previously had DPA levels lower than 0.1 ppm.

2014

Fruit from 7 new CA rooms and 5 old CA rooms were analysed monthly over 5 months for DPA residue levels. Ten samples predominantly from the old rooms had residue levels higher than 0.1 ppm

2015

Fruit from 5 old CA rooms and five new CA rooms were analysed monthly over 5 months for DPA residue levels. One fruit sample from an old room had residue levels higher than 0.1 ppm.

2016

The highest DPA residue level measured on fruit was 0.021 ppm.

Initial studies (2013) indicated that storage of untreated fruit with DPA treated fruit will result in contamination of the untreated fruit rendering them not suitable for the EU market. There is no risk of contamination from bins, pack lines and new cold stores. Initially cold stores that stored DPA treated fruit previously did pose a low risk of contaminating fruit. However, from data monitored over the 2014 to 2016 seasons it is evident that contamination risk diminished and should not be a concern. Should DPA be kept off site, there would be little to no risk of contamination of untreated fruit. There could be causes for concern if the MRL for DPA on pome fruit drop to 0.05 ppm.

The result of the ring test between the different laboratories is opposite to what were expected: to prove that the laboratories deliver the same result. Hortec had measured double compared to Hearshaw & Kinnes and almost 3 times that of Microchem. More extensive work needs to be done to compare the laboratories, especially since DPA thermofogging might be a possibility in the coming seasons.