I live in Anchorage and am an avid user of the urban trail system. On my bike commutes, I often see people foraging for large quantities of berries and leafy greens in close proximity to busy roadways. I might steal a berry every now and then, but I have always been wary of collecting in mass from areas that might be concentrating heavy metals.
I’ve had many an urban forager share their tactics to avoid concentrated chemicals: stay 52 feet from the roadway! Leaves are safe but roots are not!
A student project at Bangor University found heavy metals in roadside blackberries to be “well below any dangerous intake levels.” The University of Minnesota Extension names lead as a soil contaminant of concern, but refrains from being alarmist:
“Studies have shown that lead does not readily accumulate in the fruiting parts of vegetable and fruit crops (e.g., corn, beans, squash, tomatoes, strawberries, apples). Higher concentrations are more likely to be found in leafy vegetables (e.g., lettuce) and on the surface of root crops (e.g., carrots).”
Even in soils where lead exceeds safe concentrations, the greatest risk appears to be in consuming actual soil on the plant. Washing thoroughly is sound practice. It is also good to remember how lucky we are here to live in urban settings so close to wilderness. These natural areas will still be my foraging location of choice.