I agree with Graham Chiu about methyl bromide. According to Toxipedia, Methyl Bromide is used as a pesticide to control pest insects, nematodes, weeds, pathogens, and rodents. In the U.S., methyl bromide has been used in agriculture, primarily for soil fumigation, as well as for commodity and quarantine treatment, and structural fumigation.
It can enter your body through inhalation by air contaminated with methyl bromide.
The symptoms of inhalation of methyl bromide are abdominal pain, convulsions, dizziness, hallucinations, headache, vomiting, weakness, loss of speech and in-coordination.
But, ever since 2005, methyl bromide has not been used to fumigate pallets. There are many more things you need to consider before trying these techniques. Getting a help from landscaper would be an added advantage for you. For more info on this go here.