Dialogue: Green chemistry key to survival

Chemical researchers, especially those working for big business, have a responsibility to reject projects that will damage the planet, says TERRY COLLINS*.

Chemistry has an important role to play in achieving a sustainable civilisation on earth.

The present economy remains utterly dependent on an enormous inward flow of natural resources that includes vast amounts of non-renewables. This is followed by a reverse flow of economically spent matter back to the ecosphere.

Chemical sustainability problems are determined largely by these economy-ecosphere material flows, which current chemistry education essentially ignores.

It has become imperative that chemists lead in developing the technological dimension of a sustainable civilisation.

When chemists teach their students about the compositions, outcomes, mechanisms, controlling forces and economic value of chemical processes, the attendant dangers to human health and to the ecosphere must also be emphasised across all courses.

In dedicated advanced courses, we must challenge students to conceive of sustainable processes and orient them by emphasising, through concept and example, how safe processes that are also profitable can be developed.

Green or sustainable chemistry can contribute to achieving sustainability in three key areas.

First, renewable energy technologies will be the central pillar of a sustainable high-technology civilisation. Chemists can contribute to the development of the economically feasible conversion of solar into chemical energy and the improvement of solar to electrical energy conversion.

Second, the reagents used by the chemical industry, today mostly derived from oil, must increasingly be obtained from renewable sources to reduce our dependence on fossilised carbon. This important area is beginning to flourish.

Third, polluting technologies must be replaced by benign alternatives.

This field is receiving considerable attention, but the dedicated research community is small and is merely scratching the surface of an immense problem.

Many forces give rise to chemical pollution, but there is one overarching scientific reason why chemical technology pollutes. Chemists developing new processes strive mainly to achieve reactions that produce only the desired product.

This selectivity is achieved by using relatively simple reagent designs and employing almost the entire periodic table to attain diverse reactivity.

In contrast, nature accomplishes a huge range of selective biochemical processes mostly with just a handful of environmentally common elements.

Selectivity is achieved through a reagent design that is much more elaborate than the synthetic one.

For example, electric eels can store charge via concentration gradients of biochemically common alkali metal ions across the membranes of electroplaque cells.

In contrast, most batteries used for storing charge require biochemically foreign, toxic elements, such as lead and cadmium.

Because of this strategic difference, man-made technologies often distribute throughout the environment persistent pollutants that are toxic because they contain elements which are used sparingly or not at all in biochemistry.

Persistent bioaccumulative pollutants pose the greatest chemical threat to sustainability. They can be grouped into two classes.

Toxic elements are the prototypical persistent pollutants; long-lived radioactive elements are especially dangerous examples. New toxicities continue to be discovered for biologically uncommon elements.

The second class consists of degradation-resistant molecules. Many characterised examples originate from the chlorine industry and are also potently bioaccumulative.

For example, polychlorinated dibenzo-dioxins and furans (PCDDs and PCDFs) are deadly, persistent organic pollutants. They can form in the bleaching of wood pulp with chlorine-based oxidants, the incineration of chlorine-containing compounds and organic matter, and the recycling of metals.

The United Nations Environmental Programme International Agreement on persistent organic pollutants lists 12 "priority" pollutant compounds and classes of compounds for global phaseout. All are organochlorines.

Imagine all of earth's chemistry as a mail sorter's wall of letter slots in a post office, with the network of compartments extending towards infinity.

Each compartment represents a separate chemistry so that, for example, thousands of compartments are associated with stratospheric chemistry or with a human cell. An environmentally mobile persistent pollutant can move from compartment to compartment, sampling a large number and finding those compartments that it can perturb.

Many perturbations may be inconsequential, but others can cause unforeseen catastrophes, such as the ozone hole or some of the manifestations of endocrine disruption.

Most compartments remain unidentified and even for known compartments the interactions of the pollutant with the compartment's contents can usually not be foreseen, giving ample reason for scientific humility when considering the safety of persistent mobile compounds.

We should heed the historical lesson that persistent pollutants are capable of causing environmental mayhem, and treat them with extreme caution.

In cases where the use of a persistent pollutant is based on a compelling benefit, as with DDT in malaria-infested regions, chemists must face the challenge of finding safe alternatives.

* Dr Terry Collins, formerly of Mangere, is professor of inorganic chemistry at Carnegie Mellon University in Pittsburgh. He was invited to write this essay for the January edition of Science, the journal of the American Association for the Advancement of Science.