The World Without Us

For unclear chemical reasons, chromium is the most stubborn of all: McGrath estimates 70,000 years. Toxic in mucous membranes or if swallowed, chromium leaks into our lives mainly from tanning industries. Smaller amounts are chipped from aging chrome-plated sink taps, brake linings, and catalytic converters. But compared to lead, chromium is a minor concern.

Humans discovered lead early, but only recently realized how it afflicts nervous systems, learning development, hearing, and general brain function. It also causes kidney disease and cancer. In Britain, Romans smelted lead from mountain-ore veins to make pipes and chalices—poisonous choices suspected to have left many people dead or demented. The use of lead plumbing continued through the Industrial Revolution—Rothamsted Manor’s historic storm drains bearing ornate family crests are still lead.

But old plumbing and smelting add just a few percentage points of lead to our ecosystem. Will our visitors who arrive sometime in the next 35,000 years deduce that vehicle fuel, industrial exhaust, and coal-fired power plants spewed the lead they detect everywhere? Since no one will harvest whatever grows in metal-saturated fields after we’re gone, McGrath guesses that plants will keep taking it up, then putting it back as they die and decay, in a continuous loop.

Through genetic tinkering, both tobacco and a flower called mouse-ear cress have been modified to suck up and exhale one of the most dreaded heavy-metallic toxins of all, mercury. Unfortunately, plants don’t redeposit metals deep in the Earth where we originally dug them. Breathe away mercury, and it rains down elsewhere. There’s an analogy, Steve McGrath says, to what happens with PCBs—the polychlorinated biphenyls once used in plastics, pesticides, solvents, photocopying paper, and hydraulic fluids. Invented in 1930, they were outlawed in 1977 because they disrupt immune systems, motor skills, and memory, and play roulette with gender.

Initially, banning PCBs seemed to have worked: Rothamsted’s archive clearly shows their presence in soils dropping through the 1980s and 1990s until, by the new millennium, they practically reached preindustrial levels. Unfortunately, it turns out that they merely wafted away from the temperate regions where they were used, then sunk like chemical stones when they hit cold air masses in the Arctic and Antarctic.

The result is elevated PCBs in the breast milk of Inuit and Laplander mothers, and in the fat tissues of seals and fish. Along with other pole-bound POPs—“persistent organic pollutants”—such as polybrominated diphenyl flame retardants, or PBDEs, PCBs are the suspected culprits for growing numbers of hermaphroditic polar bears. Neither PCBs nor PBDEs existed until humans conjured them up. They consist of hydrocarbons wedded to highly reactive elements known as halogens, like chlorine or bromine.

The acronym POPs sounds regrettably light-hearted, because these substances are all business, designed to be extremely stable. PCBs were the fluids that kept on lubricating; PBDEs the insulator that kept plastic from melting; DDT the pesticide that kept on killing. As such, they are difficult to destroy; some, like PCBs, show little or no sign of biodegrading.

As the flora of the future keep recycling our metals and POPs for the next several thousand years, some will prove tolerant; some will adapt to a metallic flavor in their soil, as the foliage growing around Yellowstone geysers has done (albeit over a few million years). Others, however—like some of us humans—will die from lead or selenium or mercury poisoning. Some of those that succumb will be weak members of a species that will then grow stronger as it selects for yet a new trait, such as mercury or DDT tolerance. And some species will be selected out entirely, and go extinct.

After we’re gone, the lasting effects of all the fertilizers we’ve spread on furrows since John Lawes began hawking them will vary. Some soils, their pH depressed from years of nitrates diluting to nitric acid, may recover in decades. Others, such as those in which naturally occurring aluminum concentrates to toxic proportions, won’t grow anything until leaf litter and microbes make soil all over again.

The worst impact of phosphates and nitrates, however, isn’t in fields, but where they drain. Even more than a thousand miles downstream, lakes and river deltas suffocate beneath over-fertilized aquatic weeds. Mere pond scum morphs into algae blooms weighing tons, which suck so much oxygen from freshwater that everything swimming in it dies. When the algae collapse, their decay escalates the process. Crystalline lagoons turn to sulfurous mudholes; estuaries of eutrophic rivers balloon into gigantic dead zones. The one spreading into the Gulf of Mexico at the mouth of the Mississippi, charged with fertilizer-soaked sediments all the way from Minnesota, is now bigger than New Jersey.