Are You Testing Your Plants for Heavy Metals?
By Northeast Laboratory Services, Indoor Air Quality Department
ou don’t need an advanced degree in biology, chemistry, or biochem- istry to know that certain metals are extremely hazardous to human health. Generally speaking, everyone knows the hazards associated with Arsenic. It’s a highly toxic heavy metal that has extreme detrimental effects on living tissue. Arsenic consumption drastically increases cancer risks, damages organs, lowers IQ, and in exceedingly high concentrations is fright- fully lethal. What is not known by most is that Arsenic has many sibling elements that are just as destructive to the human body: Antimony, Thallium, Mercury, Cadmium, Chromium, Uranium - the list goes on. These elements are well known to those in the drinking water treatment business because of their low, part per billion range, safety limits set by the United States Envi- ronmental Protection Agency’s National Primary Drinking Water Regulations (pur- suant to the Safe Drinking Water Act). To growers, these fi ckle atoms are not always well known.
Y By law, Arsenic levels in public drink-
ing water must be below 10 parts per billion, Antimony below 6 parts per billion, and Thallium below an exceedingly smaller 2 parts per billion. The risk here is that,
14 ELM™ Maine - March/April 2019
in both soil and hydroponic growth, most leafy green plants take up these metals and store them within their cells. As plants take up contaminated water sources, they continue to store what is available, biologi- cally speaking the plants don’t know what to do with these metals. They can’t use them within their metabolic processes, so they are just tucked away. A hydroponic plant exposed to an EPA acceptable level of arsenic contamination, say just 1 part per billion (1/10th the allowable limit), will slowly concentrate and accumulate arsenic. Given ample time a sampling from the leafy green plant would reveal arsenic levels in the hundreds or even thousands of parts per billion.
Though the human metabolic pro- cess will react differently to absorption through the skin or inhalation as opposed to drinking water consumption, there is still a biological uptake of these heavy met- als. The very product that is consumed, in some cases, to ease or treat the symptoms of cancer may be imparting heavy metals that elevate carcinogenic risks. In terms of quality, reputable growers are certain and confi dent of their products’ purity and that
it is free of solvent and pesticide contami- nates. But are they certain it is free of these heavy metals?
Perhaps an exercise in scale is re- quired, after all what is a part per billion? In strict scientifi c terms it is a compound that exists in a ratio of one microliter per liter of aqueous (liquid) or one microgram per kilogram of solid material. In laymen’s terms this can be expressed by rounding up the entire human population of North America, putting them in an admittedly large room and asking everyone to wear a blue shirt. Now, if you wish to demonstrate what 10 parts per billion is, you would ask just fi ve people to wear red shirts instead of blue. The astronomical futility in this exercise is apparent, the numbers we are discussing are an order of magnitude so fi nite it is all but inconceivable to the human mind. We struggle to grasp and comprehend the absolute miniscule nature of these numbers. Yet, these numbers set standards and limits for safe, clean drinking water and by extension should also be ac- counted for when assessing the safety and usability of hydroponic water sources.
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