Residues remain an issue

03:11, May 11 2012
RESIDUES: A survey found high dietary exposures for dithiocarbamate fungicides, due to residues on fruits and vegetables.

In my next life I'm going to read novels. That's because I've spent so much time of this one pouring through non-fiction articles, papers, press releases and a fair amount of propaganda on the merits or otherwise of horticultural practices and food production.

Mostly it's riveting stuff, but, much as I'm compelled to read on, I often wish it wasn't quite so disturbing.

And the latest must-read is the New Zealand Total Diet Survey results, published on the NZ Food Safety Authority website, where you can discover just what you didn't know is likely to be in the food you eat.

In case you weren't aware, food in this country has been monitored for consumers' exposure to agricultural chemicals, heavy metal contaminants and nutrients every few years through the total diet survey, the latest being the seventh one since 1974.

It's used to monitor 123 commonly consumed foods available over a two-week period and assess risks associated with their consumption by age-and-gender specific groups so regulators can target and mitigate potential dangers. The foods are further divided in 61 types found nationally and 62 regionally based foods such as fresh fruit, vegetables and bread that reflect local differences in agrichemicals used or nutrient levels present.

Risk levels are based on the Acceptable Daily Intake (or ADI, see side story) for individual groups of people and individual contaminants and nutrients.


Of particular interest to me are the exposures to agricultural compound residues.

The good news, as the NZFSA tells us, is that "estimated dietary exposures to agricultural compound residues were all well below the relevant Acceptable Daily Intake (ADI)", and levels are dropping.

Of the 982 food samples screened for 241 agrichemicals in the 2009 survey, 45 per cent were found to have detectable residues, down from 50 per cent in the 2003-04 survey and 59 per cent in the 1997-98 survey. Residues of 75 different agricultural compounds were detected in the 2009 study, compared to 82 in 2003-04.

But what I always find disturbing is that the residues are still there at all.

Certainly, I concede that, given the types and historical use of some persistent agrichemicals in this country such as DDT compounds, their ongoing but hopefully diminishing presence is inevitable for years to come. But despite reassurances about tolerance levels and ADIs, I personally like to think the food I eat is contamination-free. That's why I like to grow as much of my own as possible.

But if you are buying yours you'll want to know that the food types in the 2009 survey containing the highest number of agricultural compound residues were strawberries (15 different residues), cucumber (14); bran flake cereal, muesli and grapes (12); pears and chicken takeaway (10); celery, courgette, raisins/sultanas (9); plain sweet biscuits and nectarines (8); although for each food type, these were not all in the same sample. The maximum number of residues found on any one sample was on imported strawberries.

It should be noted that 35 foods had no agricultural compound residues detected in the 2009 NZTDS, although these were largely processed, not fresh foods.

However, the survey authors noted residue detections are only an "interesting statistic", saying they have "little bearing" on the prime focus of the NZTDS and food safety risk assessment, which is based on dietary exposures.

They said the key factors in determining risk are the concentrations [my emphasis] of the residues, adding "In this regard, the 2009 NZTDS has shown that dietary exposures to agricultural compounds for all age-gender cohorts [groups] are all well below the respective ADIs, and are therefore unlikely to represent a risk to public health."

Now, if you're still with me reading this and want to know what the offending residues actually were, of the 18 agricultural compounds with the highest estimated daily dietary exposure exceeding 0.02 per cent of the ADI, three were organochlorine compounds (total DDT, dieldrin, and total endosulfan); seven were organophosphorus compounds (chlorpyrifos, chorpyrifos-methyl, dimethoate, fenitrothion, methamidiphos, pirimiphos-methyl, and prothiofos); four were fungicides (DTCs, imazalil, diphenylamine and iprodione) and four were "other" agricultural compounds (deltamethrin, carbaryl, chlorpropham and piperonyl butoxide).

The survey found "the highest estimated dietary exposures were for dithiocarbamate (DTC) fungicides, due to residues on a range of fruits and vegetables, with main contributors being apples, potatoes with and without skin, and brassicas".

Not surprisingly, one of the offending residues on potatoes was a sprout retardant, showing up not only in fresh potatoes but also in processed foods such as chips.

Most disturbing perhaps to parents of young children is that of the eight age-gender groups, the higher exposures were found for the 5-6 year children, 1-3 year toddlers or 6-12 month infants. This is because children of these ages have higher consumptions of food and energy on a per kilogram body weight basis.

The choice of eating less than perfect produce that might have a few aphids or caterpillars to wash off or losing a bit of your crop to fungal pathogens surely very quickly becomes more appealing than the potential of eating more than your share (ADI) of something much more insidious.

Check the facts for yourself at


Jobs this week include planting a few last-minute winter vegetables and getting your garden tidied up to over winter ready for planting an even bigger vegetable garden next spring.

It's not too late to plant some fast-growing greens such as silver beet, spinach, mizuna, rocket, radicchio and even lettuce for winter harvesting.

Save some of your favourite potatoes to sprout over winter and planting in early August.

Use sunny dry days for pruning and look out for unsightly scale on berry fruit canes. Prune out the worst affected canes, and if you don't want to use the traditional winter oil (mineral oil-based) spray, once leaves have dropped try spraying the scale with soybean or corn oil mixed at 2-3ml oil per 100ml water and a little liquid detergent added to help form the emulsion. The oil suffocates the scale.

Make a start on winter planting, ordering special fruit and ornamental trees from your garden centre.

May is flowering time for loquats, but situations that are frost-prone now can mean few fruit in the summer, so choose a location carefully.

Fragile blooms of the beautiful sasanqua camellias will be in full bloom now so swait until after flowering if you want to prune and shape them.