By Peter Keen
Heavy metals are a broad variety of high-density elements. They have a scary image since they include mercury, cadmium, arsenic, and lead, not exactly recommended parts of a daily diet. Plants absorb them from the soil. Today – the emphasis is added – heavy metals do not seem a problem for tea that is anywhere near the equivalent risks from pesticides.
Just about every study has found that the levels of the metals of most concern remain well below the body’s safety limits. A typical instance is an analysis of 12 tea brands in Central Europe. The World Health Organization’s (WHO) safety limit for arsenic is 1.0 milligram per kilo. The samples ranged from 0.01 to 0.25. For cadmium, the limit is 0.3 and the actual 0.001 to 0.01 mg/kg.
They are likely to become more and more part of the discussions of tea health and safety, given their growing spread and contamination of more and more areas of the environment, through industrialization. Already, there is an expanding minimarket for heavy metal detox herbal teas and supplements.
Heavy metals are toxic but often necessary nutrients: Toxicity is defined as the degree to a substance can cause damage to an organism and is dose-dependent, with a wide range of measures. Even water is toxic if drunk in large enough amounts. Six liters (13 pints) in a single dose is enough to kill a 170-lb male, through “water intoxication.” A venomous snake bite is destructive in any amount.
Many heavy metals are required micronutrients for humans and organisms, with published National Research Council RDAs (Recommended Daily Allowance), These are the level of intake of a nutrient that maintains good health. Other figures are listed by agencies to indicate safe levels.
Heavy metal molecules can bind to enzymes, cells, proteins and tissues and interfere with their functioning. That binding may build up long-term and create chronic damage rather than just acute toxicity. That has been the case with mercury, where concentrations in fish have grown at a pace where the EPA reported in 2015 that 25% of the samples tested were above the safety level. As with lead accumulation, this build up doesn’t become apparent for many years and is often revealed by the birth of a baby with deformation and damage. The short-term acute toxicity of lead is severe and demands tailored “chelation” to loosen up the binding and get the molecules moving.
A 2010 comprehensive analysis of puerh teas examined both soil, leaf and brewed tea and surveyed drinkers to identify risk factors. Concentrations were measured for aluminum, lead, cadmium, mercury, zinc, copper and arsenic. In all instances, they were well below the China safety limits expressed as a Hazard Quotient (HQ)for single elements and Hazard Index (HI) for the combination of metals. Others report that black teas have lower concentrations of metals than whites and greens, with oolongs the highest.
Long brewing times release more of the concentration. Older leaves have higher amounts, as much as 20 times that of young buds, as do most organic teas. Tap water can raise them, through their higher mineral content and, in some instances, contamination from older lead pipes. Even fine china may add toxicants.
Here is the dilemma. Tea drinkers are at risk not from what they consume but the environment that surrounds it. Auto exhaust is a far larger source of risk than tea. Today, at least, tea is not a worry.