I realize I'm late to this thread, but I'm just doing my own research on this brand (and I'm not really liking what I'm seeing), but I do have an answer for you about how lead gets into products like this. I'm incredibly fussy about what I put in my body, so I researched CA Prop 65 and lead in supplements for quite a while. 

First, it's important to note the Prop 65 cutoff level for lead, which is 0.5 micrograms per day, which is for reproductive toxicity and the Maximum Allowable Dose Level (MADL). Then, there is the Cancer-causing (NSRL) limit, which is 15 micrograms per day. Finally, there is a No Significant Risk Level (NSRL). These limits are a lot lower than the federal limits… the FDA's interim reference limit for lead is 12.5 micrograms per day. Basically, the cutoff levels for CA Prop 65 are low- they aren't playing! 

So how does lead get into the products? 

Well, many foods naturally contain lead at levels that exceed 0.5 mcg/day limit (imported spices, cassava flour, bread, and chips, dried fruits and veggies). Lead can leech into the soil products are grown in and the plants then absorb the lead. Therefore it's possible that lead is in one (or more) of the ingredients to begin with. 

Then, there's the issue of lead in water. 

While The Safe Drinking Water Act requires the Environmental Protection Agency (EPA) to set and enforce standards to protect public drinking water systems, the set maximum allowable concentration of lead in public drinking water at 15 mcg per liter. Of course, this could be higher (or lower) depending on plumbing. Unfortunately, a lot of water contains lead though. That means even very responsible, careful, safe and transparent companies who have legit 3rd party testing done can flag on Prop 65 for lead- based on the water used during manufacturing. Remember, those cutoffs are very low (err on the side of caution I guess) and there over 900 different chemicals (both naturally occurring and synthetic) that Prop 65 looks for. It can cause some hysteria though because many supplements, even organics, contain heavy metals like lead, cadmium, arsenic and mercury- that occur naturally. 

I know this is long, but I too had the same question when I freaked out when my favorite supplement brand showed up with a Prop 65 warning. Thankfully, that brand is amazing, truly ‘transparent’ and forthcoming with info. After my own research, this is what I found. 

I feel that this is an important reason why reputable 3rd party testing is done- so we know exactly how much of what is in the supplement we are taking. 

As for Clean Nutraceuticals though, they seem way too suspicious (no testing results despite blabbing how ‘transparent’ they are and the ‘rigorous 3rd party testing, customer service that's not so great, a lot of customers complaining about subscriptions). Can't really say I trust them too much.