HEAVY METALS
Residual Heavy Metals in Plant Tissue
So, how much of the heavy metal content
in fertilizers is actually absorbed and
stored in plant tissue? Well, this is a
relatively controversial, poorly understood concept. One known fact is that
some plants are hyperaccumulators
of heavy metals and some are not.
Hyperaccumulating plants absorb and
store extremely high levels of heavy
metals. Some examples are rapeseed,
bentgrass, sunflower, and duckweed.
There have been many trials to study the
finer details of this concept, but many of
them are inconclusive.
The good news, however, is that most
researchers agree the threat of toxic
heavy metal ingestion as a result of
using chemical and organic fertilizers
is very low. Most fertilizers, including many of the hydroponic nutrients
available commercially, are sold in a
concentrated form that require significant dilution before application.
Take for example a basic organic
or synthetic liquid P-K booster in
which five per cent (or 50,000 ppm)
of its concentrated composition is
made up of available phosphate.
This booster may also have trace
quantities of heavy metals
in the parts per billion
(ppb) or (ppm) range. For this
example, let’s say there
are 5 ppm (or 0.0005 per
cent of its concentrated
composition) of arsenic. The
booster’s instructions suggest diluting
the product with water at a ratio of 10
milliliters per gallon before feeding it
to your plants. At that ratio, this nutrient solution will now contain 0.013
per cent (or 130 ppm) of available
phosphate and 1.32e-10 per cent (or
0.0000013 ppm) of arsenic.
In addition, most plants are cultivated seasonally and do not have an
indefinite life cycle. As such, there
is a limited uptake capacity of these
harmful toxins due to time restraints.
What’s more, many plants are unable
to uptake many of these heavy metals
even when they are present.
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Maximum Yield USA | December 2016
“Hyperaccumulating plants
absorb and store extremely high levels
of heavy metals.”
Safety First
Even though it has been suggested
that there is a very low risk of toxicity from consuming plants cultivated
using fertilizers containing trace levels
of heavy metals, cultivators should
still aim to grow as clean as possible.
After all, many states are beginning
to enforce stricter guidelines when
it comes to harvesting consumable
crops (some will even process tissue
samples from produce before allowing it to become commercially available). Farmers have to make sure
they are knowledgeable about all
of their inputs and their combined
results. Choosing fertilizers that have
been registered by a state’s DOA
is a good first step toward peace of
mind. Additional safety measures to
take include making sure not to overfeed, using clean grow media, rotating crops, watering adequately, and
even sending in tissue samples of your
crop to a qualified lab to determine its
heavy metal uptake concentration.
Cultivators can also consider
using hyperaccumulating plants to cleanse
grow media of toxic
content. This is a particularly useful trick for soil that has accumulated heavy metals from multiple
crop cycles over time, or for groundwater cleanup. This technique is referred
to as phytoremediation and is considered a sustainable method of restoring
resources to a point where they can be
safely used again.
Don’t let fancy lingo and trendy hype
about heavy metals fool you into
wheel-spinning and hypochondriasis. Acquiring as much knowledge as
possible about your specific cultivation materials and techniques is key
to understanding consumption safety.
Integrating sustainable methods into
your operation is also highly recommended to maintain the health of you,
your plants, and the planet. Getting
a second opinion from a qualified
source is never a bad idea either.