Judging the health risks of asbestos exposure remains difficult in part because there is more than one type of asbestos and the shape and size of the microscopic fibers may alter how asbestos affects the body.

Judging the health risks of asbestos exposure remains difficult in part because there is more than one type of asbestos and the shape and size of the microscopic fibers may alter how asbestos affects the body.

But the most important factors are also the hardest to ascertain — the concentration, duration and frequency of exposure.

For example, researchers sampled air around workers in protective gear who used a front-end loader to pile dredge spoils from the banks of Swift Creek into a truck. Results showed that tackling such a task 30 times a year slightly increased a worker’s risk of cancer.

But that didn’t take into account whether the worker also walked a driveway each morning made from asbestos, or whether asbestos dust from flood sediments regularly got into that worker’s house or garden, or whether he often hiked or rode horses or drove off-road vehicles through an area that contained asbestos.

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And while the dredge spoils they loaded at Swift Creek contained up to 4 percent asbestos, the creek bed itself — which dries out in summer — has been shown to contain up to 43 percent asbestos. So if something kicked up dust from the creek while the hauler worked along the bank, that, too, could alter results.

It’s also not clear whether levels of asbestos will rise, fall or stay the same over time as more material from the landslide enters the creek.

But what is clear: The more the creek fills with material from the slide, the greater the risk of flooding downstream.

So Whatcom County and the Environmental Protection Agency are searching for ways to change the management of the creek. That may involve allowing the creek to spread more naturally or further dredging and permanently disposing of new dredge spoils. The latter could prove expensive.

Craig Welch