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Honestly, I think your best bet is to grow mint in a container you can put in the backyard and for 2 reasons. 1. mint easily gets out of hand and runs rampant in garden soil and 2. there are toxins already in the soil from years of exhaust, fuel leaks, leaded gas and paint and who knows what else so adding toxins from the air just makes matters worse. Superficial airborne pollution can be rinsed off. If your ground is polluted that is a different matter. Were old railroad ties or arsenic treated wood used in the area at one point? (Arsenic was a common wood preserver, now banned.) On the other hand, people have been growing near the road for many years. Risks vs. benefits tells me to seek an alternative if one is available and to rinse all fresh food before consuming it. Here is an article that goes over pros and cons: https://grist.org/food/is-it-safe-to-eat-veggies-grown-near-a-busy-city-street/

Mona, have you looked for tiny insects at the stem tips? This is often where aphids attack and suck juices from the leaves (or flowers). Aphids come in many colors and can be hard to find since they move very slowly. If you find some, a blast from the hose, clipping off the infested tips or applying neem oil will help. Pinching out the curled tips will also make your mint branch out and produce a nice, dense plant. Another possibility is too much water. Make sure the soil is dry an inch down into the soil before you water again. Let us know if your problem persists.

My guess would be Aphids, or another sucking insect.
Insecticidal soaps or Neem Oil can be used on Herbs safely.

https://www.gardeningknowhow.com/plant-problems/pests/insects/homemade-aphid-control.htm
https://www.gardeningknowhow.com/edible/herbs/basil/holes-in-basil-leaves.htm

This is perfectly normal, the leaves and stems are often covered in tiny hairs and have a serrated margin.

Yes, It will come back. It is a very vigorous plant. Here in zone 7, we have to watch where we plant it, as it takes over everything and cannot be gotten rid of.

I would also suggest adding dolomitic lime and wettable sulfur to the soil. This will help kill off the infection that I believe the plant has.

This article will help you to care for mint: https://www.gardeningknowhow.com/edible/herbs/mint/how-to-grow-mint-plants-in-your-garden.htm

2 options, dig them out, and/or spot spray with an organic pet safe herbicide like this one:
https://www.domyown.com/ecosmart-weed-grass-killer-rtu-p-8924.html
If you use the Ecosmart herbicide, be sure to shield the desireable plant from over-spray and drift.