Mushrooms take up nutrients and minerals from whatever they are growing on, for example, wood they’re decomposing or, in the case of mycorrhizal fungi, forest soils and tree roots. They can also accumulate toxic elements that may be present in their environment, which is a concern for people foraging for mushrooms or harvesting for commerce.
In early and late summer 2022, researchers from University of Massachusetts and Connecticut College sampled edible and medicinal mushrooms in the Connecticut River Valley of southern New England. They compared data from mushrooms growing on the forest floor or woody material at 20 sites in town or state forestland, divided into four zones (mountain, hill, valley, and coastal). At each of these sites, which extended from southern Vermont and New Hampshire to coastal Connecticut, the researchers collected mushrooms in June and again in August or September, along with soil mineral samples and samples of the substrates (forest floor or woody material) on which each mushroom was growing.
As reported in the January 2024 issue of Environmental Science and Pollution Research, the researchers found that the concentrations of nutrients and toxic elements in substrates were weakly to moderately predictive of concentrations in the mushrooms themselves. The underlying mineral soil seemed to have less relationship to what was in the mushrooms.
Concentrations also varied by location. For example, mushrooms growing in the mountains of New Hampshire and Vermont (the study’s mountain zone) had higher concentrations of mercury, while those in the Hartford, Connecticut, area (the valley zone) and near the coast had higher arsenic and cadmium. Lead concentrations showed no spatial pattern. Uptake of different toxic elements also varied among species, with those in the genus Pluteus showing higher concentrations for most toxic elements and nutrients.
The results suggest that foraging for mushrooms can be a safe activity in the southern portion of the Connecticut River Valley. Toxic metal concentrations would be a health concern only for people consuming the equivalent of 15 grams of dried mushrooms per day for the entire 90-day summer period. People can reduce exposure by consuming less, or avoiding species such as Pluteus cervinus (deer mushrooms) and Pleurotus pulmonarius (white oyster mushrooms), which had higher arsenic, cadmium, and mercury.
Average concentrations of nutrients and heavy metals in mushrooms in the study area were comparable with those documented in previous studies in other parts of the world, and in the case of mercury and lead were lower. According to the authors, “The lower toxic element concentrations in our study likely result from improvements made by policies diminishing pollution releases in the United States (e.g., the Clean Air Act, Clean Water Act, etc.) and lack of intensive mineral mining within the New England region. In addition, our study was conducted in state forests away from point-source polluters, decreasing the possibility for direct exposure to substantially toxic element concentrations.”