Risk assessment of high concentrations of molybdenum in forage

Molybdenum is toxic to ruminants when present in high levels in forage, causing physiological copper deficiency. A critical level for ruminants is 3-10 mg Mo kg^-1 dry matter. The average Mo level varies considerably between different arable soils, depending mainly on soil parent material. This study investigated the possibility of using various existing sources of geospatial information (geophysical, biogeochemical and soil chemical) to develop a geography-based risk assessment system. Forage samples (n = 173) were collected in 2006-2007. Three types of national geoscientific datasets were tested: (1) SEPA topsoil, comprising data from arable land within the Swedish environmental monitoring programme; (2) SGU biogeochemical, containing data from aquatic plant root material collected in small streams; and (3) SGU geophysical, consisting of data from airborne gamma-ray scanning. The digital postcode area map was used for geocoding, with Mo concentrations in forage assigned to arable parts of the corresponding postcode area. By combining this with the three national geoscientific databases, it was possible to construct a risk map using fuzzy classification depicting High-risk, Intermediate-risk, Low-risk and Very-low-risk areas. The map was validated using 42 randomly selected samples. All samples but one with Mo > 3 mg kg^-1 were found in postcode areas designated High risk. Thus, the risk map developed seems to be useful as a decision support system on where standard forage analyses need to be supplemented with Mo analyses.