Marijuana can be a health hazard if the plant absorbs things like heavy metals and other toxins from the soil it is grown in, the water that it gets, or pollutants in the surrounding air.
Pollutants can be carried thousands of miles from where they originated in the atmosphere, so areas that are far from industrial centers may be less than ideal.
Growing outdoors in places that are downwind of pollution centers, near heavily travelled roads, or in other places that are subject to higher levels of air pollutants should be avoided.
For soil growers, the soil the plants are grown in has to be taken into consideration. For those who purchase soil to grow indoors, local nurseries should sell soil that has been analyzed for toxins.
When growing outdoors, unless the soil marijuana is grown in is measured to verify there are no harmful substances present, there is no way to be sure.
For hydroponic or soil growers, any water that the plants get should be distilled or reverse osmosis filtered. Distilled and reverse osmosis water have virtually no impurities present.
By using distilled or reverse osmosis filtered water you can be assured that you are not consuming heavy metals or toxins that were introduced by the water supply.
Experienced hydroponic and soil growers will usually flush any nutrients from the plants in the last stages of growth. This is done by withholding nutrients.
Following these guidelines will ascertain that you are not going to produce a crop that might cause you, or people who consume your product, health problems that could have been avoided.
Soil analysis for heavy metals is not something that can be preformed at home. It can only be accomplished with expensive equipment by people who are trained to preform the task.
At the present time the only option is to pay to have soil analysis done by a laboratory that is equipped to work on analyzing soil and providing accurate measurements.
In the United States, it would cost about $50-$100 to submit a sample to a laboratory that would test soils, compost, or plant tissue for heavy metals like: arsenic, cadmium, chromium, copper, lead, molybdenum, nickel, selenium, zinc.
To Help Ensure Healthy Cannabis
1) Grow indoors or in a greenhouse and provide an air filtration system that includes a hepa filter, or something that will do a similar job of removing impurities from the surrounding air.
2) Soil can be analyzed to make sure it does not contain any heavy metals or toxins.
3) Utilize reverse osmosis, distilled, or water that is free of impurities and as close to 000 ppm (parts per million) as possible before nutrients are added, for any water the plants will get.
4) For the last stage of flowering just prior to harvest you should flush the nutrients, also called leeching, from the plant so you are not ingesting them. Instructions for flushing can be found here.