Depends on the source you get it from and if the company or manufacturer actually test for toxins. Salmon tends to be lower in heavy metals compared to other fish. If you could afford it, https://www.vitalchoice.com/products/ikura-wild-salmon-caviar offer a high quality product, but its expensive. This is another good alternative https://wildalaskasalmonandseafood.com/product/wild-salmon-caviar/. It being stored in a jar as oppose to a can may be benefical.
In terms of contamination, pretty much everything at this point is contaminated to some degree, it’s just whether or not you hear about. For example, many vegetables and grain products are contaminated with heavy metals, but you’ll never hear about it. For example, rice is loaded w/ aresnic and the deep green leafy vegetables function as bioremediators.
https://link.springer.com/article/10.1007/s13197-019-04053-5
Also, in terms of toxicity, dose and frequency are the two most important concepts to understand. I wouldn’t eat it every day, but if you are looking for a couple times a week or month, it shouldn’t be an issue. Salmon Roe is fairly high in Selenium which protect you from mecury poisioning. If you are really worried, you can take NAC as its a great chelator (extractor of mercury) and overall suporter of liver health. Anyways I wouldn’t freak out too much unless you are sick or pregnant, and even then it just depends.
https://www.tandfonline.com/doi/full/10.1080/24734306.2020.18700774
PS: It does have a solid nutrient profile w/ many benefits.
https://fdc.nal.usda.gov/fdc-app.html#/food-details/174239/nutrients
https://fdc.nal.usda.gov/fdc-app.html#/food-details/959721/nutrients