Professor Kirsten Benkendorff on the presence of chemicals in our waterways and our food

Hi Kirsten. Thanks for taking the time to speak with us. To kick off, what is your primary area of research as a Professor?

I have a PhD in Biology and Chemistry with a main research focus on healthy seafood and marine ecosystems.

Our recent social media posts on the issue of pesticide use in berry production – specifically blueberries in this case - were the most viewed and shared posts this year. What do you think that says about sentiment in the wider community?

People have a right to know what they are eating and they are concerned about the lack of regulation and testing for pesticides in fresh food they thought was healthy.

What led you to test a few punnets of blueberries from your local supermarket?

After finding a range of pesticides in our waterways and marine species, I was interested to see which were associated with intensive horticulture in our local catchment. We detected 11 pesticides below hothouses and blueberry orchards, so I was then curious about whether any were in our food.

Initially I did a preliminary test on 2 batches of blueberries and found a couple of concerning pesticides. Because I like to eat berries on my breakfast, this led me to test another 17 batches of berries from the supermarket to see how wide spread the problem was.

How did you go about doing the testing?

The berries were washed and frozen then extracted in a solvent (acetonitrile) using the QuEChERS procedure – a standard method for cleaning extracts for pesticide analysis. The extracts were then sent to a NATA accredited laboratory for multi-analyte low level detection pesticide screening using a procedure called liquid chromatography-mass spectrometry, which separates the compounds and identifies them using a mass spectrum “finger print” in comparison to analytical standards. We screened for 157 pesticides and detected 22 different pesticides across all samples

What was the greatest cause for concern for you when you eventually received the results of the pesticide testing?

I was concerned to see between 4 and 11 different pesticides in all batches of berries that I tested. We don’t actually know the cumulative or synergistic effects of multiple different pesticides on consumer health. I was particularly concerned about the levels of organophosphate insecticides in some samples: these include thiometon — a chemical than is not registered for use in Australia — as well as dimethoate and omethoate, which have been banned for use in many countries overseas due to serious health concerns.

This led me to investigate the maximum allowable residue limits set by the Australian Pesticide and Veterinary Medicines Authority in comparison with the Acceptable Daily Intake (ADI) recommended by food authorities. I found the maximum residue limits are generally high for berries and for 5 of the different pesticides I detected, the ADI would be exceeded in a 20kg child if they regularly ate more than a few berries a day at these limits.

The biggest concerns were dimethoate and omethoate: based on the concentrations I detected in 3 batches of berries, it would not be safe for a child to eat more than 20g berries per day or for an 80kg adult to eat more than 80 g berries.

In our comments section, there was some indication that the limited samples suggested testing was only indicative and not conclusive. Do you agree that a larger sample size and further testing is necessary?

In my second round of sampling, I tested 17 batches of berries (12 blueberries, 5 raspberries and 1 blackberry). These were purchased from Woolworths, Aldi, Coles and a local fruit and veggie store. They were sourced from 6 different berry suppliers in northern NSW. I think this is a pretty good representation of berries grown in our region and the results on these samples are definitely conclusive. However, there is also a need for more routine testing of a range of different fresh produce across a broader geographic area, including imported fresh, frozen and dried fruit. There is also a need for more transparency in the frequency, scope and outcomes of any Government pesticide screening programs.

How do we balance a high demand for produce and an increasing reliance on chemical use to produce our food?

Over the last 30 years, Australia has increased our use of pesticides by 234%, whilst at the same time other countries like the UK, France, Greece, Italy, Japan and Thailand have decreased their use by 25-80%. This demonstrates that it is possible to move towards lower reliance on pesticides with good integrated pest management programs.

The overuse of pesticides not only leads to resistance, but it also kills many of the natural predators. It will take a while for the ecosystem to re-balance, but some short-term loss can lead to long term gains in productivity. This needs to be supported by good legislation, education and incentives to help farmers transition.

Furthermore, there will be less reliance on pesticides if our food is grown in season and in climates suitable for the type of plant. For example, blueberries originate from a cooler temperate climate in northern America. Whilst some varieties have been adapted to grow in subtropical climates, the warmer humid environment is associated with more pests and fungal diseases. In particular, we have fruit fly in NSW and Queensland, but not in Tasmania where berries are also grown. Consequently, I would expect less dependance on organophosphate insecticides in berry orchards in Tasmania.

It is also important to note that pesticides are known to degrade soil health – so over a long time period, productivity will be lowered by the overuse of pesticides. This is likely to be the biggest problem for large scale monoculture. Our agricultural industries need to consider long-term sustainability to meet future demand rather than immediate productivity and profitability. This means investigating alternative systems that are both productive and maintain soil health.

In an ideal world what do you see as the best way forward when it comes to food production?

We need better regulation of pesticides that prioritises consumer and environmental health. If food can’t be grown profitably without a heavy reliance on pesticides, it is being grown in the wrong way and/or in the wrong place. Mixed horticulture and integrated pest management, including more research on biological controls, will help reduce the reliance on pesticides. These agrichemicals should never be used preventatively on a large scale. More support should be given to help farmers transition away from pesticide dependence toward spray free and organic production.

Better awareness and education on pesticides use is also required across the community to allow people to make informed choices. Food production industries need a social license to operate, as markets are driven by consumer demand. 

Improved government regulation and monitoring of pesticides is also essential. It should not take so long to review and phase out pesticides that have already been banned overseas due to human health and environmental concerns.

We need to take a precautionary approach to all pesticide use that priorities health even when there is uncertainty about the impacts. If we always have to wait until there is conclusive proof of harm, too much damage will be done before change is implemented. The long-term costs to society will be far greater that any profits gained from growing food a bit more cheaply with pesticides.