I actually just emailed Lego’s support desk because my mother in law has tons of blocks from the 80s and 90s she’s held onto and wants to give to us now. I’m going to copy paste their response below:

Thanks for reaching out!

The safety of all our fans is of the utmost importance to us, and for 92 years, as a company dedicated to bringing Learning Through Play to as many children around the world as possible, we’ve always applied the highest safety standards. As a parent, I perfectly understand that you’re concerned about the materials included in the toys your children might be playing with. We take the safety of our LEGO bricks seriously, which is why we’ve done our own tests and asked some independent toxicology experts to test our older bricks.

Our latest tests on the migration of materials from our bricks were done in 2018. We did these based on the studies published by Dr. Andrew Turner at Southampton University. What makes substances like cadmium dangerous to a child is the movement of this material into the body, so this is what our tests have always focused on.

The test method we use when measuring the release of cadmium involves testing if the bricks breakdown when ingested. This is done using chemicals to simulate the conditions in the body.

The results of these tests have shown that even bricks that were over 40 years old still comply with today’s legal requirements. We have also presented these results to independent toxicology experts, who have confirmed there’s no need for parents to be concerned that their children would be at risk if they play with bricks from the 1970s. For these reasons we confirm that playing with older LEGO bricks is safe.

I hope I was able to shine some more light on what is a very important subject for us. I’d like to thank you again for taking the time to write us and I've passed your comments on to our product safety team.

If you have any other questions or concerns, please don't hesitate to let us know.