Thursday, February 18, 2016

Cadmium and Arsenic update: soil tests from CCLC

One big unknown in the controversy about heavy metal pollution in southeast Portland (OR) has been the amount of accumulation of pollutants identified by the Oregon Department of Environmental Quality as above its benchmark levels in air. Cadmium (Cd) and arsenic (As) were measured well above emissions benchmarks at an air monitoring station near the Bullseye Glass production facility; while those emissions were not particularly high with respect to health risks for inhalation, we did not know if the pollutants had accumulated in soils. For heavy metals this can be a real concern, as atomic elements like Cd and As do not convert into other substances as a molecular pollutant can. There has been a legitimate concern that even air concentrations that were not acute could have built up to dangerous levels over the functional lifetime of the Bullseye facility.

Now we have some illuminating data, in the form of soil testing results from the very close Children's Creative Learning Center, about 150 meters away from the Bullseye factory. The report from testing is posted here, and I've included the data table below:

Helpfully included in the test results are background levels for the Portland area. The 6" and 12" designations refer to the depth at which soil was sampled at each of six sites around the CCLC campus. The table also includes DEQ soil screening values for residential areas. Not included are the DEQ risk-based concentrations (RBCs) for urban residential areas, which are 1.0 mg/kg (As) and 160 mg/kg (Cd).

So what do the results tell us? First off, that there's no evidence for an overall accumulation of arsenic at the site, since the averages at both depths fall below the background level for the City as a whole. It is true that sites 5 and 6, which are on the west side of the building, are a bit higher than the other samples, especially at the 12" depth; this could be an effect of proximity to Bullseye, or even just proximity to a nearby road. Sample #4, however, is immediately adjacent and shows lower As levels, especially at 12" depth. The values do fall above the DEQ's risk-based concentration of arsenic for soil ingestion, skin contact, and inhalation through contaminated soil, with the RBC set to match the 1 in 1 million risk of causing a cancer. The average value at 6" depth would correspond to roughly a 1 in 70,000 increase in the change of developing a cancer using assumptions like roughly year-round exposure. The maximum at 12" would correspond to a 1 in 20,000 increase in cancer risk with similar assumptions.

For cadmium, the sample values are more consistent from location to location. At depth, they fall very close to the background for Portland, though at 6" they are about twice that value, so there may have been some accumulation of Cd in the soil. The values are all very far below the risk-based concentration from DEQ for soil (by a factor of 50 or more), so there appear to be no grounds to worry about a health risk for cadmium from soil at CCLC.

Incidentally, you may have noticed that the DEQ screening values (the RBCs) are really different for the two elements; at first I thought that the value for cadmium was a typo! But the big difference seems to be that arsenic is volatile (i.e. it can evaporate into air from soil) while cadmium cannot, along with the fact that arsenic is more easily absorbed through the skin.

So what is the overall conclusion? I hesitate to generalize too much, but the amounts of As and Cd measured at CCLC all fall within about 2X the background for the Portland basin as a whole. For arsenic, only at the 12" depth are samples well above that background. Conversely, for cadmium, the values at depth are near baseline, while the shallow samples are elevated. The difference could be due to different leaching rates for the two elements, or they could represent different modes or times of accumulation. So there may be some accumulation of these elements from nearby industrial operations like Bullseye. On the other hand, this is for a very close site to the Bullseye factory; given the relative values observed in the moss and lichen study from the US Forest Service, soil levels much farther away are likely to be at background levels for the City if soil concentrations drop at a similar rate to moss and lichen concentrations. As an example, airborne Cd levels drop by a factor of about 2 by the time one reaches Cleveland HS or Winterhaven Elementary in the moss and lichen study; if soil accumulation drops off at a similar rate, those schools would be expected to have soil levels of Cd and As near the background levels. For students and staff at CCLC, continued exposure to unremediated soil may be unwise, but health risks from soil will be small for arsenic and negligible for cadmium.

UPDATE: The Oregonian has released their own set of soil testing data here. The levels tend to drop off quickly with distance from Bullseye, with a few scattered high results among mostly below-detection-threshold tests. One very high test result near Cleveland HS should probably be followed up, though as an outlier it is likely to come from another source than settling from Bullseye. A high lead level next to Powell Blvd. is likely (IMHO) to be the result of years of auto traffic using leaded gasoline.


  1. One interesting point about the table above is that the DEQ screening level for arsenic is much lower than the background levels in Portland. That is to say that even pristine soil in Portland, untouched by human hands, contains more than 10x the arsenic level that DEQ considers "interesting".

  2. Yeah, that difference between the two metals is striking. FWIW, the DEQ level for a "hotspot" requiring remediation is 43 mg/kg, twice the max measured at CCLC. I'm not sure if the background rate is "untouched by human hands", however; there could have been some arsenic pollution before the background was measured. But it does rather skewer the naturalistic fallacy - that what is natural is inherently good (think about natural radon emissions if you need another example)!

    1. There is no shortage of examples of naturally occurring cancer hazards, sadly.

  3. Duncan,
    Thanks for putting up the soil test results and for your involvement in adding data, interpretation and context to the issue at hand.

    Are the specifics from the soil tests at Winterhaven released yet? While the data from CCLC is useful, it is one data point. More information would be useful to avoid the effect of geographical anomalies, biases in wind patterns. Nearness to Bullseye is a useful shorthand but the DEQ map of exposure(based on the concentrations in moss/lichen).

    Does anyone maintain a central repository of test results as they come in?
    Thanks again,

  4. Michael - I'm not aware of a central repository that is public; myself, I just put up results as I find them - if they are detailed enough to analyze. Readers should feel free to link to other data sets in the comments...this isn't the best place to centralize stuff, but it's better than nothing!