It is important that you buy from a reputable supplier who manufactures to high standards which includes ensuring that there are no high concentrations of heavy metals (HMs).
An example of such products with heavy metal come from the Kore Organic Watermelon CBD Oil Tincture, this was found to have enough metal toxicity to cause lead poisoning!
Ref: https://www.miamiherald.com/news/health-care/article242796336.html

So what exactly are heavy metals?
Heavy metals are essential metal which exhibited a high density and of which some are highly poisonous in small concentrations. However, some are termed as essential nutrients for example zinc, which becomes dangerous if consumed in high dosages.
Why should I be concerned about heavy metals when buying CBD?
The answer is to firstly educate yourself and then also know how to buy from a reputable company that will not sell unsafe products.
A good cbd brands will have been manufactured to the highest food grade standards to ensure that not only are there no heavy metals, but also other contaminants, solvents and fillers.
At the end of the day you are consuming these products and will want the peace of mind that what you are taking is doing you good rather than the opposite.
Also, it is not just about what happens at the manufacturing level but also at the growing level too. Hemp plants are extremely good at cleansing soil, so if grown in heavily polluted fields you could risk for heavy metals to be passed through the food chain and ultimately to you!
The most common heavy metals found to cause health risks found on some CBD product
There are two types of heavy metal poisoning that can occur, from sudden single dose poising and gradual poisoning that occurs over time. In both cases symptoms of vomiting, headaches, tiredness, aching and loss of consciousness may occur.
Lead poisoning – seizure, confusing and reduced fertility including miscarriages.
Mercury poisoning – damage to the heart, lungs and immune system.
Arsenic poisoning – cancer, skin lesions and cardiovascular disease