It’s not going to do much harm unless ingested.
Was the sample taken from milk or something?
Probably soil. And from soil- hay and other animal feeds and from meat/dairy products - ingestion.
From Wikipedia:
Together with caesium isotopes 134Cs, 137Cs, and iodine isotope 131I it was among the most important isotopes regarding health impacts after the Chernobyl disaster.
Strontium-90 is a “bone seeker” that exhibits biochemical behavior similar to calcium, the next lighter Group 2 element. After entering the organism, most often by ingestion with contaminated food or water, about 70–80% of the dose gets excreted. Virtually all remaining strontium-90 is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues. Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia.