We recently purchased some Lawn Food for our grass and as I went to store it I read the packet and am a bit concerned about the following statements:

... It releases essential nutrients to simultaneously promote greening, healthy lawn growth, root development and resistance to stress and fungal disease.  It also contains organic ingredients which will break down slowly ensuring lawns receive nutrients for months...

WARNING - Use of this product may result in cadmium and mercury residues in excess of the Maximum Permissible Concentration (MPC) in plant and animal products and may result in accumulation of these residues in soils.


NPK 11-1-5 plus polyacrylamide wetter

Nitrogen (N) as ammonia    8.3%
             (N) as organic       2.7%
Total Nitrogetn (N)             11.0%

Phosphorus (P) as water soluble      0.2%
                  (P) as citrate soluble    0.06%
(P) as citrate insoluble                     0.2%
Total Phosphorus (P)                        1.0%

Potassium (K) as chloride                 4.8%
(K) as organic                                   0.2%
Total Potassium (K)                           5.0%

Sulphur (S) as sulphate         11.0%
Calcium (Ca)                         2.0%
Magnesium (Mg) as sulphate  0.3%
Iron (Fe) as sulphate             0.45%

... Apply at a rate of 90 grams over 3 square metres.  ... Apply every 3 months except during winter...

Why would it have such a warning?  I am now worried that we may have used this brand before...  Besides the children running, crawling and playing on the grass I also now have chickens that are allowed to free range there and we are eating the eggs.

Hopefully I am totally paranoid, but would appreciate your opinion on this warning and if anyone knows if it is on *all* fertilisers or just some.  For some reason I am thinking that it might be very common on the slow release type ones which I have also used in the past. 

Without spending heaps on soil analysis, how worried should I be about the fact these have been used in the past - anyone know how long it takes for Mercury/ Cadmium levels to come back down (if they are up of course) to dissipate *hopefully this is the right sort of context* from soil? 

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  • I knew that this is often a problem with turf management on golf courses (never swim in those water holes on a golf course! they're like a toxic soup!!) but I didn't know/ remember why. I always though it was to do with lawn grub etc pesticide application. So I googled it :)

    Wikipedia says this: http://en.wikipedia.org/wiki/Fertilizer

    Heavy metal accumulationThe concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru[48] and the Christmas islands[49]) increases the contamination of soil with cadmium, for example in New Zealand.[50]

    Uranium is another example of a contaminant often found in phosphate fertilizers (at levels from 7 to 100 pCi/g)[51]. Eventually these heavy metals can build up to unacceptable levels and build up in vegetable produce.[50] (See cadmium poisoning) Average annual intake of uranium by adults is estimated to be about 0.5 mg (500 μg) from ingestion of food and water and 0.6 μg from breathing air[52].

    Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead[53]arsenic, cadmium[53], chromium, and nickel. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.[54][55] Concerns have been raised concerning fish meal mercury content by at least one source in Spain[56]

    Also, highly-radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues; tobacco derived from plants fertilized by rock phosphates contains Polonium-210 which emits alpha radiation estimated to cause about 11,700 lung cancer deaths each year worldwide.[57][58] [59][60][61][62]

    For these reasons, it is recommended that nutrient budgeting, through careful observation and monitoring of crops, take place to mitigate the effects of excess fertilizer application.

    Mercury usually accumulates in the aquatic food chain. So I'm guessing your fertiliser contains fish/ bone meal and mined phosphate minerals.

    OK, so
    a) don't worry, safe for kids and chooks. You would have to use it a LOT to get a dangerous build up
    b) lock it up with organic matter like Anthony says - or top dress with compost, compost water or worm wee
    c) buy a fertiliser that only contains organic ingredients (certified)
    d) try these: dynamic lifter, compost, worm wee, rooster booster, blood and bone. Note pelletised manure products are basically slow release
    e) rake your lawn to remove thatch build up
    f) aerate your lawn by pricking it all over with a pitchfork before you chuck the dynamic lifter/ worm wee about
    g) top dress with compost = best thing you can do for it
    h) see if you can get clover or another legume to grow amongst your grasses - they fix nitrogen and feed your lawn

    Remember that non-organic products are made of distilled petrol. They actually hurt the micro-organisms and worms. Like getting photo developing chemicals on your hands. Good levels of soil bacteria and worms are plant fertilisers themselves - you just need organic matter to provide food and habitat for these helpful beasties.
  • Hi D, the warning are fairly common practice labeling for this kind of product.
    To be safe water in some Humic acid and EM this will encapsulate the metals and Em will help to oxidise them.
    If you haven't done this to much"eg a few times since you have been there" the build up will not be anything to worry about.
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