Toxic Metals in Camellia sinensis: Analytical Methods, Human Health Risk and Regulations.

Persistent toxic substances tend to accumulate in the environment owing to anthropic activities, causing increasing detrimental to food safety. Toxic metals are among the most deleterious pollutants because they concentrate on all environmental matrices, in particular, those involved in the food chain where the consequences on human health may be irreversible. Nutritional supplements, including herbal extract, vitamins, mineral salts, botanical remedies, are certainly an integral part of the food chain. For this reason, great attention has been focused on tea leaves (Camellia sinensis), widely used by the world's population to obtain drinks, generally by infusion. It should decidedly be emphasized that the concentration of toxic metals in tea should be under the maximum limits allowed by law. The problem is that in the international legislation, laws specifically concerning the tea do not exist. The existing laws, in fact, provide legal concentration limits for leafy vegetables in general, and only for a few metals. Obviously, this is a problem that should be solved, above all by extending the maximum allowable concentration limits to an increasing number of toxic elements, but also by increasing the number of types of plants. Moreover, only in a few cases, regulations provide safe limits, but the analytical techniques useful to check for those limits are not indicated. The present work proposes an exhaustive focus on what are the metals of interest, and what is the state of the art about analytical methodologies suitable to detect these toxic metals in Camellia sinensis. For all metals or group of metals, various analytical techniques and procedures employed are critically discussed. Particular attention is paid to the analytical performance, in terms of accuracy and detectability. A separate section is dedicated to the analytical procedure for the determination in Camellia sinensis of new emerging anthropic toxic polluting metals: platinum group metals (platinum, palladium, rhodium, osmium, ruthenium, and iridium) and thallium. This discussion would also be a stimulus to solicit International Organizations to fill the gap of the lack of strict and comprehensive laws regulating the maximum allowable concentrations for an increasing number of contaminants in this matrix, especially considering their enormous daily use.