Summary: This limited study indicated that a slight deposition of metals (Copper and Manganese) may have occurred in one agricultural field, but the increases measured in the surface samples were likely insignificant relative to normal background levels for these soil types. Other sites showed no increase in heavy metals on the soil surface. Regardless, the bottom line is that the concentration of metals measured were within normal ranges for all soil types evaluated.
Background: A lithium battery fire began on January 16, 2025, and released smoke and ash that contained the heavy metals, cobalt, copper, nickel, and manganese into the atmosphere. Coastal soils naturally contain these elements; however, the public was concerned that ash deposits may elevate heavy metal concentrations in agricultural fields closest to the battery fire, which could potentially be a food safety concern. In response, we evaluated if these specific heavy metals increased above native concentrations in soil collected from agricultural fields near the site of the fire.
Procedure: Soil samples were collected from agricultural soils in the vicinity of the Moss Landing battery fire to determine if deposition of ash increased cobalt, copper, nickel, and manganese concentrations on the soil surface. Soil samples were collected on February 10th and 11th, 2025. Samples were collected from fields that had not been disturbed by tillage since the fire. Light rain fell on three occasions between the fire and soil sampling. Ten subsamples of the soil were collected from three locations at each site and composited from depths of 0 to 1 inch; 3 to 4 inches; and 0 to 12 inches. The sample from 0 to 1 inch depth would presumably contain potential deposition of metals onto the soil. The 3-to-4-inch depth was collected below the soil surface and therefore would not contain and deposit ash but assumed to have an equivalent concentration of metals as the soil surface sample prior to the fire. Hence the 3-to-4-inch sample provided a pre-fire concentration of metals to compare against the concentration measured on the soil surface. The 0 to 12” soil sample integrated the concentration of metals in the first foot of soil and provided a measure of the average concentration of these metals in the soil. In addition to analyzing the soil samples for cobalt, copper, manganese, and nickel, soil pH was also measured to provide an indication of the solubility of these metals in soil, and therefore their availability for plant uptake and potential leaching. Generally, these metals are not readily available for plant uptake in soils with a pH greater than 7.5. Soil samples were air dried and sent to the UC Davis Analytical Lab for analysis of total metal content utilizing a nitric acid/hydrochloric acid closed vessel microwave digestion. Analysis of the metals was by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The data were analyzed for statistically significant differences in analyte concentration by location and depth using SAS software.
Results: Table 1 shows the results of the seven sites that were evaluated. The six sites closest to the battery fire site were 1.30 to 1.83 miles away. An additional site 17.1 miles from the battery fire site was also included for comparison. No sites had statistically significant greater levels of cobalt on the soil surface than the concentration measured at the 3-to-4-inch depth. Given the high soil pH values measured in 5 of the 6 sites close to the fire, it was not likely that any metals deposited on the soil surface would be soluble enough to move deeper in the soil with the rain events that occurred prior to when soil samples were collected in February. In that respect, we have good confidence that the lack of elevated levels of cobalt on the surface relative to the 3-to-4-inch soil sampling layer indicates no significant deposition of cobalt occurred at these sites. In addition, all sites were within range for the average concentration range for cobalt in soils in California (Table 2).
Nickel was found to be higher in the surface soil compared to the 3-to-4-inch depth at 3 of the 6 sites closest to the battery fire site, but lower in 2 of the sites, and the differences between the concentration in the surface soil and deeper were not large enough to be statistically different. The background levels of nickel in the soils sampled varied substantially from site to site indicating differences in the minerology of the parent rocks from which the soil developed. However, none of the soils had concentrations of nickel that would be of health or a food safety concern.
Only site 6 had a statistically significant increase in copper and manganese compared to the concentrations measured in the 3-to-4-inch depths. However, the increased concentration in copper was less than 1 ppm relative to the layer below. The increase in concentration of manganese on the soil surface was 19 ppm at site 1, which was a 4% greater concentration than in the 3-to-4-inch layer.
All other sites, including the one furthest from the battery fire, did not have any statistically significant increase in metals on the surface soil, and the concentrations were within the normal ranges for these soil types.
Table 1. Levels of metals in three layers of the soil of six sites close to the battery fire and one farther from the site for comparison. Each measurement: n=3.
Table 2. Levels of metals from two sites on Watsonville Loam soil from Santa Cruz County and statewide ranges of the metals.*
*Bradford, GR, AC Change, AL Page, D Bakhtar, JA Frampton and H Wright. 1996. Background concentrations of trace and major elements in California Soils. Kearney Foundation of Soil Science, University of California Division of Agriculture and Natural Resources Special Report.