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Chemicals, Not Overfishing, May Be Cause of Lake Trout Decline

Compiled by Mary Beth Doyle
January/February Issue, 2004

A team of researchers has determined that dioxin and similar toxic chemicals were high enough in Lake Ontario to kill virtually every lake trout that hatched there from the late 1940s to the late 1980s. Their findings differ from traditional explanations for the collapse of the lake trout population in Lake Ontario that focus on overfishing and attacks by the parasitic sea lamprey.

The researchers found that lake trout, in their early life stages, are among the most sensitive fish to dioxin, PCBs, and other similar chemicals. At concentrations as low as 30 ppt (parts per trillion) dioxin in egg tissues, mortality of newly hatched fish exceeds normal rates.

Because they are retained in tissues, dioxin, PCBs, and similar chemicals bio-accumulate up the food chain. Animals near the top of the food chain, like lake trout, generally have the highest concentrations of such chemicals in their body tissues.

Using mathematical models, the researchers estimated that dioxin levels in lake trout eggs reached the 30 ppt mortality threshold in the early 1940s. By the late 1940s, concentrations reached 100 ppt. At that concentration, 100% of juvenile trout can be expected to die, the authors reported. By 1982, environmental regulations had sufficiently reduced toxic contamination levels so that egg concentrations had dropped to the point that no measurable direct mortality from dioxin was expected.

“That’s the good news of the study,” said Dr. Philip Cook. “It shows that pollution regulations really can be effective.”

Cook points out, however, that researchers know much less about so-called “sub-lethal” effects of contaminants on lake trout, doses that do not kill the fish in laboratory tests but do impair critical functions like vision or swim bladder inflation.

Cook PM, et al., “Effects of aryl hydrocarbon receptor-mediated early life stage toxicity on lake trout populations in Lake Ontario during the 20th century,” Environmental Science and Technology, Sept. 1, 2003.


Low-Sulfur Fuel Key to
Lower School Bus Emissions

Student exposure to air pollution from diesel school buses can be cut by 90% if school districts use ultra low-sulfur fuel and add soot traps. That’s a preliminary finding from a diesel school bus study conducted by the American Lung Association of Metropolitan Chicago.

The study measured the diesel exhaust students are exposed to on a conventional school bus compared to a bus using ultra low-sulfur fuel and retrofitted with emission-reduction equipment.

On a typical bus ride, researchers found children are exposed to up to five times as many diesel emissions as they would encounter on a retrofit bus. The conventional school bus generated up to 200,000 diesel particles per cubic centimeter inside the cabin compared to a maximum of 40,000 in a retrofit bus.

“School bus riders are often exposed to a high level of diesel exhaust,” says Dr. Edward Naureckas, Assistant Professor at the University of Chicago and a board member of the American Lung Association of Metropolitan Chicago. “Diesel fumes are known to be harmful to humans and are probably carcinogenic, so we need to do everything we can to reduce the amount of diesel emissions inhaled by young children.”

In a typical bus-stop scenario, researchers found diesel exhaust levels exceeded 500,000 particles per cubic centimeter as the accelerating bus passed a departing student. The retrofit bus never exceeded 40,000 particles.

Particulate matter – a major component of diesel exhaust – has been linked to a wide variety of serious health issues from upper and lower respiratory infections, asthma attacks and possible asthma onset, to heart attacks and premature death. More than 60% of airborne particulate matter from mobile sources comes from diesel exhaust.

The City of Ann Arbor and University of Michigan are both using ultra low-sulfur diesel for their buses, and have implemented programs to install particulate traps and catalytic converters in their buses (see Greening Initiatives Gaining Ground in Ann Arbor Schools, From the Ground Up, Aug./Sept. 2003).

The final ALA study is scheduled for release in March 2004. For more information on the diesel bus study go to www.lungchicago.org.

Compiled by Mary Beth Doyle, M.P.H.,
Ecology Center Environmental Health Campaign Director

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