DIY ECM WASTE AND TOXICITY TO ALGAE FORMATION (observation)

I've had ECM waste in a bucket in my backyard for at least 1.5 years. Recently UV exposure degraded the lid enough for it to crack and alloy the environment in side the bucket. On observation algae has grown in the bucket.

It appears that the salt and any dissolved metal ions (such as Cr6 ) are not in concentrations high enough to inhibit algae growth or natural selection has allowed for the reproduction of algae that can tolerate these toxins.

Does anyone know of a DIY way to test if this is super algae or if the ECM waste contains toxic metals?