Formaldehyde Solution Effectively Inactivates Spores of Bacillus anthracis on the Scottish Island of Gruinard

Gruinard Island was heavily contaminated with the spores of virulent Bacillus anthracis during biological weapons trials in World War II. However, an extensive survey in 1979 showed that most of the island was not contaminated. In the early 1980s, a more intensive survey revealed that the contamination was largely confined to the top 8 cm of the soil in a 2.6-ha area of the 211-ha island. Small-scale tests showed that the spores could be inactivated by drenching the soil with fluid biocides. A solution of 5% formaldehyde in seawater applied by surface spray to each square meter of ground was shown to be the most effective treatment and was utilized for large-scale decontamination of the affected areas. Following this treatment, extensive sampling revealed that most of the spores of B. anthracis had been inactivated. Isolated pockets of surviving spores were treated further. A flock of sheep was then allowed to graze over the entire island for 5 months; none contracted anthrax.