All really big unknowns at this stage....
I work in the environmental industry, previously in Australia I used to do mostly contaminated land/groundwater assessments. Australia, and Victoria in particular, is quiet well legislated regarding enforcing water/groundwater standards based on end use, such as drinking water, irrigation, stock watering or contact recreation, with the majority of the guidelines taken from USA EPA threshold values. The studies which inform these also inform food safety authorities.
Data for these limits are derived from various sources such as tests on cells in the lab, long term exposure studies on animals, or incidental exposure studies of humans and populations which are very limited due to the ethical restrictions of exposing people to known or suspected toxic compounds.
The issue then is that a high standard of evidence for the threshold values is required for them to be scientifically robust. The take away being that the values set mean something tangible, the downside being that many compounds that don't have sufficient evidence despite being known or suspected toxicity lack safe threshold values. Some of which are described as "likely carcinogens" but have no scientifically determined "safe" threshold limit in drinking water.
One well documented compound in plastic, BPA, which is implicated in the issue of increasing prevalence of microplastics, is a good example, it's a known endocrine disruptor, however there is no tangible safe level that has been derived. This article does a pretty good job of explaining the issues involved...
https://www.theguardian.com/lifeandstyle/2018/feb/19/are-we-poisoning-our-children-with-plastic
basically we do not know what the implications are long term.