Toxicity from Metals, Old Menaces and New Threats

Metals make up the bulk of the periodic table and range from the very light (e.g., beryllium) to the very heavy (e.g., the actinides). Metals are important constituents of life, drive economic activity and industry, but can also be a hazard to human health. The metals can be roughly divided into three groups. The first being those metals, such as iron and zinc, that are essential to human life and have a wide therapeutic dose range. The second group of metals, such as lead, mercury, and uranium, has no known biological role and are toxic even at low doses. The third group of metals, such as selenium and manganese, has a role in maintaining human health but has a very narrow dose range that, when exceeded, produces toxic effects. A quick look at the periodic table also shows us that there is a very rough correlation between the atomic weights of metals and their toxicity. The heavier the metal the more likely it is to be toxic, and while there are exceptions (for example, beryllium is very light and also very toxic) this rough correlation has driven our view of the relative risk of metals for many years. The approach of using atomic weight as a guide to toxicity seemed to work in the period of early industrialization when lead and mercury were being used in abundance and this concept was reinforced with the birth of nuclear power when heavy metals were again seen to be very toxic and, additionally, radioactive. In contemporary society the correlation between metal toxicity and atomic weight is no longer useful [1]. For one, we have come to understand that many of the lighter metals, such as aluminum, can be toxic. Additionally, industrial processes have moved new metals and combinations of metals into the environment. Gallium arsenide, for example, is used extensively in the microprocessor industry yet a Pub Med search yields only, at this writing, 37 articles addressing its toxicity, which in the world of toxicology means that it has mostly been ignored. Rechargeable batteries use a variety of metals to perform their function, yet despite calls for recycling, most end up in landfills with the potential to release nickel, mercury, cadmium, lithium and other substances into the environment [2].