As expected, the concentration of pesticide residues and the associated
risk were especially high in unprocessed tomatoes stored for only
three days, whereas storage and processing reduced the risk of adverse
effects considerably. The relatively rapid decay, with DT50 values of
0.85–1.65 days,was most likely partly due to a combination of hydrolysis
and microbial degradation, as none of the organophosphates are
known to be particularly volatile (British Crop Protection Council,
2014). Chlorpyriphos, dimethoate and malathion all have documented
hydrolysis rates in the range of 0.5–6 days depending on pH (British
Crop Protection Council, 2014), indicating that hydrolysis might be an
important degradation pathway under the humid storage conditions.
In addition, all five organophosphates have reported half-lives in soils
of a few days, indicating that microbial degradation on the surface of
the unwashed tomatoes could also be of importance (British Crop
Protection Council, 2014). The organophosphate half-lives in this
study are, however, in the very short end of literature values for environmental
degradation, particularly considering the cool storage conditions,
though degradation half-lives of chlorpyriphos residues in apples
of b1 day have been reported (Knight and Hull, 1992). Hence, it cannot
be excluded that physical removal of the pesticides to the paper bags
that the tomato sub samples were kept in during storage have played
a role in the decrease of the pesticides over time