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Opinion: The long-term poisoning of our rural soils with the heavy metal cadmium threatens vast tracts of rural land and will soon affect the exportability of crops and animals says scientist Mike Joy


By Mike Joy*

Imagine if someone told you that over the last 70 years we had systematically contaminated large areas of New Zealand’s very best agricultural and horticultural soils with a toxic, carcinogenic heavy metal and that as a result we will be unable to grow food for human consumption on large tracts of this land from now on? 

I’m guessing that you would very likely and reasonably respond with utter disbelief and anger.

It is appalling but sadly true, appalling not just that it has happened but that it continues almost unabated.

The heavy metal is cadmium and the culprit is intensive farming and horticulture and bizarrely it’s not just you who hasn’t heard of this but almost all of the farmers who own the land as well.

I can already hear the predictable and patronising response from industry and government to this news that they have covered up for so long, that pollution is a necessary cost of feeding the world and saving our economy.

But that response is bizarre, obviously once we have poisoned the soil we will feed no one.

The reality is that now our options for feeding ourselves, let alone the rest of the world in the future have been drastically reduced

Of course this contamination wasn’t intentional at least not in the beginning - we just poured on phosphate fertiliser to grow more stuff.

The problem is that cadmium does not readily leave the environment so even incredibly small amounts add up over decades.

This is especially true in intensively farmed areas like the Waikato where now more than 160,000 hectares are contaminated to the point that would have been officially labelled as a contaminated site. It can no longer be classed as contaminated because changes to legislation this year removed agricultural land from any contamination classification, an interesting way to get rid of the problem.

Fortuitously for the dairy industry cadmium doesn’t get passed to milk or we would have been banned from export markets decades ago.

Instead of going to the milk cadmium accumulates in the body like it accumulates in soil.

In mammals it accumulates in the major organs (kidneys and liver).

As a result, the sale of these organs from cattle and sheep over 18 months old are banned for human consumption in New Zealand. 

The problem for humans is that vegetables take up cadmium from the soil so this carcinogen is ingested by us when we consume those plants and then slowly builds up in us. It’s very hard to decide on a safe level of cadmium in soils to keep our intake below danger levels. Currently food standards are used as a guide, the theory is that if soil cadmium is kept below a certain level it should mean that in vulnerable crops like potatoes, onions, root and leafy vegetables and most grains, the standards will be met and we will be safe. 

We know very little about the health effects of long-term cadmium accumulation so the supposedly safe levels of consumption are changing globally.

However, if we use the European standard then the latest results of our 5 yearly total diet survey, horrifyingly shows that New Zealand toddlers, infants and children already eat cadmium at, or near, the limit and the rest of us are not far behind.  The World Health Organisation standard is more lenient and New Zealand uses this limit so the figures look a bit better.

Of course using these more lenient guidelines might backfire if New Zealand standards are not accepted by Europe it could have potentially huge ramifications for our markets there. 

There is no good news for the future either, the national cadmium report produced by government revealed that on-going cadmium accumulation in our agricultural soils has the potential to increase dietary intakes in the New Zealand population. 

So what has the fertiliser industry and government done about this issue?

Apart from producing a national strategy and setting up a working group dominated by industry representatives virtually nothing has changed in the four decades since cadmium accumulation was first identified as a problem. 

Not surprisingly given the industry domination of the working group there is no evidence of net reduction in the rate of contamination.

Every year, about 2 million tonnes of superphosphate fertiliser is applied to pastoral and horticultural soil in New Zealand, so that means we are adding a whopping 30-40 tonnes of cadmium per year. 

One distressing aspect of this debacle is how industry and government have kept the truth about this issue from the public and even worse, from farmers. Undoubtedly because of the potential economic consequences on land values and maintaining growth in production the lid has until now been firmly kept on this sad reality. 

The security of food production in New Zealand for exports, and for feeding the nation, depends on us facing up to this crucial issue.

Public perceptions of the value of New Zealand’s dairy boom are slowly changing with the realisation of the social and environmental costs become more obvious.

Many people are now aware of the multiple impacts on our lakes and rivers, but only a tiny minority know that we are poisoning our soils as well.

The freshwater issues in rivers can be repaired easily, once you stop putting nutrients and sediment in them they will clean up in no time, contaminated soil however is almost impossible to fix.


Dr. Mike Joy is the Director of Massey University's Centre for Freshwater Ecosystem Management. You can contact him here »

We ran a story on the soil cadmium problem in 2011 and you can find it here »




Thank you for publishing this Stunning that this has gone on really. While I am aware of depleted aquifers and mineralisation from irrigating crops, but I didn't realise we are trashing godzone this way.


Easy answer - farm battery hens!

Mike, what about our vegetable gardensn in the cities.  Are they contaminated too and if so how do we test our gardens and if tests are positive how do we rectify the situation?

A 50-300 year timespan before serious levels of cadmium are reached?  How can you reconclie that with the report in Mike Joy's article that (using European standards) infants tested in NZ are at the maximum recommended level and the rest of us not far behind? 

Thanks for answering.  

all well for cattle and sheep. But what about vegetable crops? That is what the article seems to be saying are more dangerous for human consumption at present Cd levels

The application of vast tonnages of chemical fertilizer, super phosphate, for the last 80 odd years on the highest production farm land is NZ has been full hardy at least or criminal ? This article may well have legs, time will tell.

Your right on that one MIst42nz - wasn't the advice coming directly from our own Ministry of Ag?

Makes you think, eh:
This article caught my eye because I was involved with a project to find an alternative material for one that contained cd. The requirement was that no amount of cd was acceptable. The material and applications concerned were non-ingestible.

This is the most disturbing fact of the article - what could the government be thinking of? - denial of this and other possibly related soil contamination issues through legislation is a most heinous crime against humanity -  was it undertaken without our consent to facilitate the sale of land to foreigners at the behest of the banks or did the pressure emanate wthin the farming communities, or both? - we need urgent answers as life preservation is obviously not up for discussion.

Big Thanks.

CTNZ - There is an enormous amount of evidence against GMO's and thankfully now a huge amount of scientific peer reviewed papers on the effects from consumption of GMO's.
It was Kissinger who said "Control the oil you control the nation, control the food and you control the people" .   Andrewj's post yesterday quoting Ayn Rand comes to mind again.
I think farmers are very aware of the issues CTNZ, most, especially family farmers don't want to ruin their own livelihoods or the next generations and so remain good stewards of the land.

This article brings up an issue that the certifiers of Organic properties has been addressing for some decades.
One question does come to mind though; where do the 'contaminated' animal organs end up if not fit for human consumption? Byproducts destined for pet food, or blood & bone to be used as a fertiliser? I am already aware that the latter needs chemical analysis before being allowed as an input on certified organic properties.

Sounds bad - but I have just learned that if you smoke cigarettes you have a 4-5 times high blood cadmium level. Sleep peacefully if you are a non smoker - glad I gave up a year ago!
Wikipedia source

Soil scientists have been nervously watching the heavy metal build up in our soils for decades. I sat through the lectures.
Clearly what we need to do is rezone all rural land to residential and cover it in cheaply built houses that sell for 500k. Think of the money we could all make, we'll compound the house prices up at, say, a totally reasonable 5 to 15% pa.
And we'll import our food from China. With ideas like this I really should be PM, or at least FM.

Like mist42nz stated there are other sources of low cadmium phosphate fertiliser on the market. The cost per unit of P is not that much dearer than superphosphate. Currently the low cadmium phosphate is imported subject to demand and product availability. If the demand was there consistently then I’m sure it would be imported in larger and consistent quantities.

Great stuff.  However some useful facts and figures would be nice.  Perhaps a table with natural levels, current levels, levels in different types of fertiliser, increase rate (per application, per 10 year period), leach rate and stripping rate (crops, wool, meat), what exactly are the WHO and EU safety guidelines.
  If I understand the article and the comments Cadmium is increasing due to the use of Phosphate fertiliser, what is the origin of this Phospate?  Some, such as 'upnorth' comment that 'low cadmium' phosphate is available but this is not 'no cadmium' so cadmium is still being accumulated just at a slower rate, so what is the solution? 
Plants take up cadmium and animals eating those plants concentrate it in the liver and kidneys.  Therefore when I concentrate plant material (compost) and use this to fertilise my vege patch I am accumulating cadmium in the vege patch.  Equally when I bury hares, possums and other animal wastes in the orchard I am accumulating cadmium at those sites.  What is the solution?
So is there a 0% cadmium fertiliser?  How much cadmium is there in poultry manure, fish meal, seaweed, lawn clippings?
We have a stand alone sewage treatment facility, "Clearwater", and are very careful about what enters that system.  Is the waste water from that also contaminated with the heavy metals naturally excreted from our bodies?  If so then that must also be poisoning the drainage field.
Finally, different species of plants are known to accumulate heavy metals (and other poisons) at different rates.  But then it may be more important to maintain a varied diet and maintain Vit.C levels for the chelation benefits.