You Must Remember Fish
PCB-tainted lake fish still stealing memories
THURSDAY, June 7, 2001 (HealthDayNews) -- People who ate lots of fish from contaminated waters decades ago could be having memory lapses today, says a new study.
The problem stems from fish laden with polychlorinated biphenyls (PCBs), a toxic chemical widely used in electrical equipment and hydraulic fluids until banned in the late 1970s because it can cause cancer, says University of Illinois researcher Susan Schantz.
Before it was banned, the chemical had seeped into waters and contaminated fish, which were eaten by sports fishermen and their families. Experts say children were most susceptible to its effects because of their developing neurological systems.
Now many adults also are showing the effects of that contamination, says Schantz, a toxicology professor.
"Primarily verbal memory and learning seem to be affected. This isn't a generalized problem. It's specific to a certain aspect of cognitive function," Schantz says. Attention span, planning ability and fine motor function (small, precise movements) don't seem to be affected, she says.
"Our results are actually pretty consistent with what's been seen in children and in animal studies," she says.
One earlier study found children born to women who'd eaten considerable amounts of fish from Lake Michigan have lower IQs, as well as problems with memory and attention span.
The new study focused on 180 people living along the eastern shore of Lake Michigan, which was especially hard-hit by the PCB menace. The subjects all had been recruited in 1980 for Schantz's earlier research and were revisited between 1992 and 1995, when their ages, ranging from 49 to 86, averaged 64.
Schantz says 101 people had been big fish eaters until at least 1980, consuming roughly 24 pounds or more a year. The other 79 people ate about 6 pounds of lake fish a year.
Those who'd eaten the most fish and thus had the highest levels of PCBs in their blood had the most trouble with recall, Schantz says.
For instance, the researchers read a short story or paragraph to a participant and then asked the person to recall it immediately and again, unexpectedly, 30 minutes later.
People with high PCB levels did all right with the immediate recall but fared the worst 30 minutes later, the study says. They also had similar difficulty with what Schantz calls semantic clustering, which is a memory tool people generally use to recall lists of similar things. Given a shopping list of such items as fruits, spices and tools, for example, most people group items together by their meaning when trying to remember them, she says.
But that didn't happen with the people with higher PCB levels, she says.
"We can't say for sure that the reason they couldn't remember the stories as well was because they weren't using [semantic clustering], but the fact that they're not using that strategy as much suggested to us that there might be an underlying problem affecting their memory," Schantz says. The findings appear in the June issue of Environmental Health Perspectives, a journal of the National Institutes of Health.
Just how PCBs affect memory remains a bit of a mystery.
"There's laboratory research going on, trying to figure out what the mechanisms are, what PCBs do to the brain. We don't have a good handle on that yet," Schantz says.
The fallout from PCBs is not a problem that's likely to disappear anytime soon, says Milton Clark, health and science adviser with the U.S. Environmental Protection Agency (EPA) in Chicago.
"We estimate roughly about 100 years before fish advisories will be lifted. PCBs break down so incredibly slowly, and the Great Lakes don't exchange waters very rapidly," Clark says.
Lakes, unlike rivers, can't really cleanse themselves, he says. "Lake Michigan changes its water every 99 years," Clark says.
"Millions of pounds of PCBs found their way into Lake Michigan," Clark says. PCB levels in the lake "declined fairly dramatically, about a 10-fold decrease in almost 10 to 15 years," because of the passage of time and clean-up efforts, he says.
"Now they've leveled off, though, and the levels we still have in fish would be somewhere around 50 times higher than what would be acceptable for a high level of human consumption," Clark says.
"We think the leveling off is due to the fact that you still have sediment reservoirs [around various rivers that feed into the lake], and they still leech PCBs out into the lake," he says.
Schantz says contaminants like PCBs "get into an aquatic ecosystem like the Great Lakes and just sit there, not broken down."
"Mammals can't metabolize them, so they accumulate in our body fat. Even if only small amounts are in our food, levels [in our bodies] will accumulate eventually," she says.
"This will be with us for decades," she says.
But not every fish eater needs to worry about the problem.
The Food and Drug Administration has set limits on what it considers safe levels of PCBs in foods.
"There are small amounts of PCBs in many foods that we eat -- fish, meat, dairy products," Schantz says. "But you will not have any undue exposure [to this contaminant] from commercial fish, fish from the grocery story or restaurants."
"It's the sports-caught fish [that are worrisome]," she says. "There aren't laws that say you can't go out and catch that fish."
What To Do
To find out whether it's safe to fish in a river or lake near you, check with your state health department or the latest Fish and Wildlife Advisories issued by the EPA.