Contaminated water in pesticides could be source of norovirus entering the supply chain, finds study

The possibility of pesticides being a source of human norovirus (hNoV) depends on the presence of viruses in the water used to reconstitute the pesticides, the potential of viruses to persist in reconstituted pesticides, and by the number of viruses adhering to the edible parts of the produce.

Farmers use various water sources in production of fresh fruits and vegetables, including well water and surface water such as river or lake water, sources which have been found to harbour hNoV, according to previous research.

In a separate development the European Food Safety Authority (EFSA) has said residue compliance rates remain high in its annual pesticide report.

Fresh produce and Norovirus link​

The consumption of fresh produce has been associated with outbreaks of hNoV but it is difficult to identify where in the supply chain the virus first enters production, said a team of researchers.

Pesticides are commonly applied in the production of produce just before harvest to optimise product quality and extend shelf life.

To prevent contamination of fresh produce, knowledge of the possible introduction sources of the viruses, such as water, is needed to implement appropriate and efficient preventive measures.

Possible source​

The researchers studied the persistence of hNoV GI.4, hNoV GII.4 and murine norovirus (MNV-1), the only culturable norovirus, in eight different pesticides after 0 and two hours.

Virus concentrations were determined by reverse transcriptase PCR, and infectivity of MNV-1 was determined by endpoint dilutions followed by maximum likelihood estimations.

Chemicals were diluted in a concentration equal to the smallest volume used (200 L/ha) to equal the highest pesticide concentration used in practice.

“​The application of pesticides may therefore not only be a chemical hazard, but also a microbiological hazard for public health,” ​said Verhaelen et al.

A promising approach to minimize the microbiological health risk of pesticide application, not depending on compliance and awareness of farmers, is the inclusion of antiviral substances into pesticides, concluded the researchers.

EFSA pesticide report​

Meanwhile, EFSA’s annual report on pesticides in food, found that more than 97% of samples contained residue levels that fall within permissible limits.

MRL exceedance rates of foods imported into the EU, Norway and Iceland were more than five times higher than those of foods originating in these nations - 7.9% compared to 1.5%.

MRL values for organic food commodities in the EU are identical to those for non-organic foods.

Analysis of 3,571 organic food samples showed an MRL exceedance rate of 0.8%, said EFSA.

EFSA concluded that there was no long-term risk to consumer health from the pesticide residues through their diets.

However, in assessing short-term acute exposure, the report found that a risk could not be excluded for 0.4% of samples – or 79 out of 18,243 based on a worst-case scenario of consumption of the largest portion of a food type that contains the highest residue in each pesticide.

The fourth annual report gave an overview of pesticide residues found in food in 2010 in the 27 EU Member States, as well as Iceland and Norway.

Source: International Journal of Food Microbiology​​

Online ahead of print, doi: 10.1016/j.ijfoodmicro.2012.11.007

“Persistence of human norovirus in reconstituted pesticides — Pesticide application as a possible source of viruses in fresh produce chains”​

Authors: Katharina Verhaelen, Martijn Bouwknegt, Saskia A. Rutjes, Ana Maria de Roda Husman