Scary about the welding incident.
I probably would not use the product, given what is known about the risks, except that I have used it many times before with no side effects.
But it makes you wonder if there could be a cumulative problem.
Even though zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption.[144] The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish.[156] The Free Ion Activity Model is well-established in the literature, and shows that just micromolar amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all Daphnia in water.[157]
The free zinc ion is a powerful Lewis acid up to the point of being corrosive. Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post-1982 American one cent piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.[158]
There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/d; a recent trial had higher hospitalizations among elderly men taking 80 mg/day.[159] The USDA RDA is 15 mg Zn/d. Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or to adversely affect cholesterol.[144] Levels of zinc in excess of 500 ppm in soil interferes with the ability of plants to absorb other essential metals, such as iron and manganese.[80] There is also a condition called the zinc shakes or “zinc chills” that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials.[107]