>My question is are there now enough safeguards in place that we're unlikely to be repeating the same mistakes?

Nope. For instance some of the chemicals in sun screen never had to pass rigorous safety testing because it was assumed they couldn't enter the blood, but in fact that's not the case, and already at least one is known to have negative effects on reproductive health: https://jamanetwork.com/journals/jama/fullarticle/2733085 . Who knows what other chemicals are floating about in various cosmetics entering the bloodstream through the skin without ever being safety tested for that.

Not to mention that many kinds of sunscreen have chemicals in them that kill Coral reefs. It's becoming fairly common for ocean tourist communities to pay attention to, but that won't really stop whatever washes down the rivers.

For chemicals that cause illnesses that take decades to show up, it's my guess that we will never find all of them, and there are likely a lot of them out there. It's a hard problem. Maybe it can be helped by using modelling techniques to extrapolate effects over time.

> are there now enough safeguards in place that we're unlikely to be repeating the same mistakes?

I doubt it. One obvious example is plasticizers: there was a big ruckus about BPA a few years ago, so manufacturers phased it out and switched to different plasticizers, many of which are incredibly chemically similar to BPA. It's seems very plausible that they have similar negative health effects, but there's no regulation (or even disclosure, in most cases) of which plasticizers are being used.

https://www.science.org/content/article/bpa-substitutes-may-...

TCE was originally conceived as a replacement for chemicals such as chloroform and ether, which were deemed to be too toxic to the liver for anesthesia. Once the toxicity of TCE was discovered, it started being phased out in various industries.

For degreasers, it was replaced by 1,1,1-Trichloroethane, a chloroalkane later banned by the Montreal Protocol. It's use in refrigeration was replaced by 1,1,1,2-Tetrafluoroethane, a hydrofluorocarbon banned in the EU today for global warming potential. And finally, its use as a general anaesthetic was succeeded by Halothane, which doesn't seem to have any major health affects (beyond those coming from being an anaesthetic). However, that too was later replaced by Sevoflurane, which is suspected to accelerate Alzheimers.

Also both those anaesthetisc are greenhouse gases.

So no, we are definitely going to have more problem chemicals in the future, because chemistry is complicated.