Here, leaching plastics may not be the primary source of the newfound global marine contaminant
SAN FRANCISCO — Chemists have been showing for years that bisphenol A, an estrogen-mimicking building block of polycarbonate plastics and food-can coatings, can leach into food and drinks. But other materials contain BPA — and leach it — such as certain resins used in nautical paint. And Katsuhiko Saido suspects those paints explain the high concentrations of BPA that his team has just found in beach sand and coastal seawater around the world.
At the last ACS national meeting, Saido showed that Styrofoam and related polystyrene-based materials can degrade in seawater and taint the coastal environment with styrene, a toxic building block of the foams. When he announced his styrene findings last September, reporters asked him: What about BPA? Does this potentially toxic breakdown product of the widely used plastics also show up at the beach?
He hadn’t a clue. So he went back and reanalyzed samples of seawater and sand that he had collected for the polystyrene study. And sure enough, BPA was there. Sometimes in fairly substantial quantities, he now reports. Of the 28 sites sampled, he found BPA at all, often at values in seawater at or near 100 parts per billion in Puerto Rico, Guam, Japan, Korea, Taiwan and the Philippines. Concentrations of BPA were orders of magnitude higher in sand. For instance, they exceeded 50 parts per million on a French beach and ranged closer to 100 ppm on sandy shores in East Asia, Florida and Costa Rica.
But the hot — especially boiling temperatures — shown to break down polycarbonates in many food-chem studies don’t exist at the beach. So Saido went to the lab to see how low he could go and get the plastics to leach BPA. His starting materials: polycarbonate baby bottles that he purchased from around the world. He initially measured the amount of free BPA that was available to leach out of them. Values varied widely — from about 40 ppm (an Italian bottle) to 102 ppm (a Chinese bottle). The major exception: The U.S. baby bottle he assayed had a measly 11 ppm free BPA.
Saido removed this ready-to-leach BPA from the plastic in a Japanese baby bottle and discarded it. Then he put a small piece of this cleaned up polycarbonate into a flask so that he could link any BPA that emerged to its breakdown — not to unbound BPA in the starting plastic. Slowly, he heated the plastic in a bath of polyethylene glycol at any of several temperatures. All it took was cooking the plastic for five days at 50 degrees Celsius (122 degrees Fahrenheit) to begin breaking polycarbonate’s chainlike structure apart, releasing individual links of BPA. It's hot but not an impossible temperature to reach outdoors.
“This study shows that at 50 °C, under the sun, polycarbonate is not stable,” according to Saido (speaking through an interpreter, a California-based former grad student). Presumably it the breakdown could occur at even lower temperatures if they persisted long enough.
Initially, Saido thought degrading trashed plastics, like the baby bottles, might have been a source of the marine BPA pollution. Now he's dubious. Saido says he suspects it's certain resins in ship paints. And because the BPA concentrations he's turned up in the coastal environment “concern him,” he’d like to see more research done on the use of these epoxy resins in the marine world.
But there’s probably a lot more polycarbonate wastes entering the environment than epoxy resins, so it makes sense to find a good way to recycle those plastic goods before they degrade, releasing BPA. Toward that end, Saido is actively developing technologies to transform polycarbonate wastes into liquid and gaseous fuels.
Saido, K., et al. 2010. New Global Ocean Contamination Derived From Marine Debris Plastics (Abst. Div. of Analytical Chemistry #180). American Chemical Society national meeting, San Francisco (March 23).