Heavy metal plants

Herbal medicine is a global phenomenon, a multibillion dollar industry, and its raw materials phytochemicals are widely used as the precursors for regulated pharmaceutical products. One problematic area on both sides is in product purity, with contamination by toxic heavy metals one of the most common complaints.

Now, researchers in Argentina have developed a digestion method for improving outcomes in heavy metal determination for quality control of herbal medicines using ETAAS (electrothermal atomic absorption spectrometry) and USN-ICP-OES (ultrasonic nebulization system coupled to inductively coupled plasma optical emission spectrometry). Their initial tests show the approach is viable for heavy metal determination in phytochemical extracts. A trial on the widely available St John's wort remedy (Hypericum perforatum), considered beneficial in mild depression, demonstrated no excessive heavy metal contamination with values well below World Health Organisation recommended safe limits.

María Gomez, Soledad Cerutti, Lorena Sombra, María Silva, and Luis Martínez of the National University of San Luis point out that metallic elements are often natural constituents of plant compounds with biological activity but can represent either essential or toxic activity in metabolism. However, contamination with heavy metals of the environment in general, from diverse pollution sources, such as industrial and traffic emissions, and agricultural expedients including cadmium-containing dung, organic mercury fungicides, and the insecticide lead arsenate, means that contamination represents a potentially increased health risk.

Problems such as kidney failure, liver damage, and chronic toxicity might arise from long-term use of contaminated products. A quick and simple approach to assaying phytochemicals for quality control purposes is essential. Gomez and colleagues explain how ETAAS, ICP-OES, and ICP-MS are widely used for heavy metal testing, but their sensitivity is not necessarily compatible with the low levels of heavy metals that might be present in samples.

For this reason, the team has turned to ultrasonic nebulization system to improve sample preparation following work by colleague Rodolfo Wuilloud and his team at the University of Cincinnati. They tested the approach on various samples of H. perforatum and were unable to detect chromium or cobalt in either liquid or solid samples, whereas aluminium, cadmium, lead, iron, and vanadium were found in almost all samples tested.

The team concludes that their digestion technique significantly improves heavy metal determination in phytopharmaceutical samples. "The simplicity and versatility of the procedure makes it attractive for its use in the pharmaceutical quality control of medicinal plants," the researchers say.