Its best to have a hygienist such as Heggies check it out and give a report to the state and safety of the sheets.

I had a tenant 2 years ago take action against an owner over some fibro found in the back yard 4 foot underground and the owner spent around $3800 to have the pieces tested  as well as the soil, when the report come back as safe, the matter was thrown out of the CTTT. If you have a legal report that it is safe then you have met your obligations but should always have it checked on