Plumbing the origins of lead in nature.

Lead has played a role in human society for thousands of years. Romans made pipes of it. Medievalists made goblets of it. Armies made bullets of it. Artists and builders made paints with it. And, automotive engineers added lead to gasoline to make engines run better. The problem is: lead is a poison.

Lead was long used for pipes, and the word, plumbing, is derived from the Latin word for lead, plumbum. At least one environmental chemist has suggested that the demise of Roman civilization was exacerbated by lead poisoning. The lead concentration in tap water from ancient pipes in Rome was more than 100X greater than in spring water nearby.

When lead is smelted from its primary ore, galena, lead vapor and particles are emitted to the atmosphere and transported globally. The layers of ice in Greenland contain a record of the deposition of lead from the atmosphere, which shows an early increase about 2000 years ago. With the onset of the Industrial Revolution, lead was transported through the atmosphere from the industrialized countries in the Northern Hemisphere to the remote Southern Hemisphere. Thus, in the Indian Ocean, concentrations of lead are much higher in surface samples of seawater than in samples from the ancient deeper waters.

The emission of lead to the atmosphere reached a maximum in the mid-20th century, when tetraethyl lead was found in nearly all gasolines. Bromide compounds were added as well, so that the lead would pass through the exhaust system as lead bromide, and not clog up the engine. Roadside soils accumulated toxic concentrations of lead. French wines show a peak in lead concentration in 1962, and a decline thereafter as leaded gasoline was phased out. Lead was deposited in New England forests, where it accumulated in small mammals and in the organic layers of the soil, where it may take decades to wash out. The isotopic composition of lead in the Greenland icepack contains the fingerprints of the lead from gasoline, transported for 1000s of miles.

Various compounds of lead were added as pigments to paints. I grew up in a white clapboard house in a Cleveland suburb, and as a kid I remember feeling how heavy a can of leaded house paint was. Even the yellow paint on pencils contained lead pigments.

Lead poisoning first showed up in young city children who ingested chips of paint. And, those who chewed on their pencils during a difficult arithmetic test also got a dose. Exposure by inhalation was noted, as urban air contained lots of lead bromide aerosols from automobile exhaust. By the early 1970s, it was clear that lead in the blood of urban children was leading to undesirable health effects, including mental retardation. In the U.S., lead is now prohibited in paint, gasoline, and most plumbing fixtures.

At least one use of lead remains widespread: its use in ammunition and the weights in fishing tackle. Spent shot and lost tackle accumulate in wetland sediments where waterfowl feed. A few years ago, the U.S. Fish and Wildlife Service estimated that 3% of waterfowl succumbed to lead poisoning every year, so lead shot is now prohibited for duck and goose hunting. Lead weights are prohibited for fishing in several northeastern states.

The history of lead pollution is the opening chapter in the history of human impacts on global biogeochemistry. Now, we’ve removed the lead from many products, and the environment is cleaner as a result. I recently gathered up all my old leaded fishing tackle and took it to a metal recycling center.

You can do the same, and do your best not to release “heavy metals,” such as lead, mercury and cadmium, to the environment.



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