How we tested Columbia River salmon for contaminants

Oregon Public Broadcasting and ProPublica reporters conducted interviews and hearings with tribal leaders, toxicologists, and public health experts, many of whom became informal advisors throughout the project. Tribal leaders have expressed their support and interest in additional testing of the fish. Based on these conversations, the reporters developed a preliminary methodology for testing salmon for toxicants in a stretch of the Columbia River. This methodology followed standard fish tissue testing methods. Reporters sent this methodology to the same informal advisors for review.

A reporter bought 50 salmon from tribal fishermen upstream of the Bonneville River, in the area of ​​the river designated for fishing under the tribal treaty. The majority of the fish were Chinook salmon, with two coho salmon and one steelhead. Fish caught in late September 2021. With salmon in hand, a reporter gutted the fish, removed the heads, and cut it into pieces to put into five coolers. Fish were placed on ice in five different coolers, with 10 fish of approximately the same size placed in each cooler.

The fish test can be performed on the whole body of the fish, on fillets with the skin on or on fillets with the skin removed. Although fish head is consumed by many people, particularly in tribal communities, reporters asked the lab to test fish fillets with skin because it was determined to capture the best approximation of what is often consumed in tribal diets.

A reporter sent the fish samples to ALS, an accredited laboratory, and followed ALS protocols for sample collection and delivery. The lab combined the fish to create five new composite samples, each one containing 10 fish. (Creating composite samples allows more fish to be tested without increasing lab costs.) ALS technicians then ran tests to assess the levels of 13 metals and two classes of chemicals in each of the five fish samples. In March 2022, ALS sent an analysis report to OPB and ProPublica that included case narratives, chain of custody and test results, which we shared again with experts and public health officials as we developed a plan to analyze the results.

As a first step, the reporters performed quality assurance checks on the test and data processing. In doing so, the journalists encountered limitations in testing that prompted them to make two standard choices in both national and international approaches to testing for fish toxins:

  1. ALS has been tested for general mercury, yet methylmercury is the most important form for general health. The EPA and the European Food Safety Authority assume that 100% of the mercury from fish tissues is methylmercury. Journalists have adopted the same approach.
  2. ALS has been tested for arsenic, yet inorganic arsenic is the form most important to overall health. The reporters found that there was not much coherent approach to determining inorganic arsenic without testing it directly. Idaho’s Department of Environmental Quality recently launched a sampling effort in which researchers found that, on average, about 4% of the arsenic in fish is inorganic. The department’s study is one of the most robust examinations of inorganic arsenic concentrations near the Columbia River. The Oregon Health Authority is taking a different approach. They will initially assume 10% of the arsenic is inorganic, said David Freer, a toxicologist at the agency, and if results indicate levels could harm human health, they will re-analyze any remaining sample specifically for inorganic arsenic. If this is not possible, the Ministry of Health will not use the data at all. Given these uncertainties, the OPB and ProPublica chose not to proceed with a cancer risk assessment of inorganic arsenic since news organizations had not specifically tested for it.

The reporters then calculated the average concentration of the chemicals across each wet weight sample. They then evaluated how these results compared to standards from the Environmental Protection Agency, the Oregon State Health Authority, and the Washington Department of Health.

Of the 13 metals and two categories of chemicals tested, three contaminants exceeded federal and local standards at various levels of fish consumption: mercury, or methylmercury; polychlorinated biphenyls, or polychlorinated biphenyls; and dioxins/furans.

Reporters shared their methodology and findings with experts for review. Toxicologists from the Oregon Health Authority and the Washington Department of Health, as well as former and current EPA scientists, reviewed the results and, in some cases, performed their own calculations to assess how the test results compared to their own standards. The reporters then met with each of these individuals to talk through the results, ask and answer questions, and eventually update their results to include feedback. The experts’ observations were consistent with each other. This process led to the finding that concentrations of mercury (methylmercury) and PCBs would justify the EPA and at least one state health agency recommending no more than eight 8-ounce servings of salmon per month. The equation used for these calculations can be found in the Oregon Health Authority report (page 4) and the Washington Department of Health report (page 35).

At the same time, the OPB and ProPublica calculated the estimated cancer risks of eating salmon with the levels of contaminants present from our tests. For each pollutant, a reporter calculated exposure levels for multiple scenarios based on how different populations ingested, including the general population intake and the average and high rates of the Columbia River Tribes, which were based on consumption surveys. The amount of contamination assumed in this calculation is taken from the upper 95% confidence level of the test results. Current and former EPA scientists have revised the methodology and calculations.

To calculate the lifetime risk of cancer, the dose of a potential carcinogen must be multiplied by the cancer potency factor, which estimates toxicity. Cancer potency factors, also known as regression factors, were obtained from this EPA report. Former and current EPA officials, as well as an epidemiologist, reviewed the accounts and findings.

We also took into account the following consideration: Per EPA guidance, when calculating safe levels of exposure to various chemicals, the agency calculates monthly limits for the exact number of meals a person should eat. But then it rounds that up to a multiple of four in an effort to make risk communication easier to follow. For example, if one finds out that levels of dioxins would ensure that someone would only eat five fish per month to avoid cancer risks, that would be rounded to the four fish per month.

Ultimately, this led to the finding that, based on the levels of dioxins in our samples, anything more than four 8-ounce servings of these tested fish each month could lead to an increased risk of cancer beyond the Environmental Protection Agency’s (EPA) standard of 1 in 100,000. This means that if 100,000 people are exposed to these levels of pollutants, one of them may develop cancer as a result of the exposure.

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