Lead - Heavy metal neurotoxin. While Rockwool's airborne lead emissions are small compared to other pollutants, no amount of exposure is safe for children and this must be fully vetted.
CO2e - Carbon Dioxide Equivalent. Not harmful.
HAPs - Hazardous Air Pollutants. WVDEP Fact Sheet/Preliminary Findings
The main health issue for working with rockwool is that it may pose an inhalation hazard when dry. When it is wet, there is no inhalation hazard. The EPA has this to report: “Most studies in humans have not shown an increase in cancer from exposure to glasswool, glass filaments, rockwool, and slagwool. Animal studies have reported an increase in lung tumors in animals exposed to ceramic fibers by inhalation, while no increase in tumors was reported from exposure to glasswool, rockwool, or slagwool. The EPA has classified refractory ceramic fibers as probable human carcinogens. The International Agency for Research on Cancer (IARC) has determined glass filaments, glass wool, rock wool, and slag wool to not be classifiable as to their carcinogenicity to humans (Group 3).” EPA
HOWEVER, research from the Mesothelioma Justice Network has found other past research has linked several diseases with the inhalation or ingestion of some forms of mineral wool. Based on this research, mineral wool health risks include:
“The effects of the fibers of glass wool and stone wool can be compared to those of asbestos. In the past, we did not know asbestos was very dangerous. The results of the effects of fibers in glass wool and mineral wool are only being seen right now, so we must deal with it carefully,” said Dr. Marjolein Drent, professor of interstitial lung diseases at Maastricht University.
How To Protect Yourself From Mineral Wool
The National Institute for Occupational Safety & Health (NIOSH) treats mineral wool like a hazard and still maintains the recommendations that were put into place in 2000 before mineral wool was determined “safe.”
According to NIOSH, workers should protect themselves by wearing:
NIOSH also tells workers not to eat, drink, or smoke anywhere near a work site with mineral wool, and to prevent dust from dispersing. Just remember, ROCKWOOL POSES INHALATION HAZARDS WHEN DRY
COMPOSTING USED ROCKWOOL
While the Cannabis Horticultural Association (CHA) has never promoted the use of rockwool for horticultural purposes, it does recognize its widespread use and would like to at least draw awareness to the fact there are methods of composting rockwool. The next section covers 2 methods of composting and 1 trial result provided by a industry representative to provide a framework of understanding how to recycle rockwool via composting. ***The biggest concern we have with rockwool, is that it poses a VERY DANGEROUS INHALATION HAZARD WHEN DRY. It is important for anyone wishing to engage in these practices to understand this. It is of grave concern that farming practices that till the soil with composted rockwool might be exposing themselves to potential inhalation hazards.
1. Generator (Grower) Preparation
• Spent rockwool must be free of all potential contaminants including plastics (no clips, no
twine, no plastic sleeves), trash, etc.
• If spent rockwool has excessive moisture, it should be allowed to dry out for a few days
(dependent on climate conditions and weather). However, excessive dryness is not
desired since the rockwool will eventually turn into a dust or powder which can
become airborne. Ideal condition is "not too wet, not too dry".
• If the grower has a tub grinder or even a wood chipper, the spent rockwool can be
ground up (size reduced) with other green waste and organic materials. This is not
required of the grower but will help in reducing the volume and weight of the material.
2. Green Waste Processor (Composter)
• Spent rockwool can be sized to a 1/4 minus screen using your existing compost
grinders, augers etc.
• Composters should incorporate 10% rockwool to 90% green waste ratio by weight. The
product breaks apart quite easily, and at 10% mixture, the rockwool will not be visible.
• By adding additional granulate (up to 25%), it can also lighten the bulk density of the
compost product depending on the level of compaction. In general, large particles (>1
cm) will ventilate the compost while finer particles (<1 cm) may increase the water
3. Results from Composting Trials Using Spent Rockwool
• End of life Grodan rockwool, along with vegetation, including roots is an acceptable
feedstock for windrow composting at the 10% rate.
• The compost from the Grodan windrow was indistinguishable from other compost
produced at this facility.
• This feedstock met our quality standards and would fall under the definition of
Agricultural Materials in Title 14(California).
• Process: Windrow composting. Equipment Used: Vermeer TG7000 tub grinder and
Doppstadt 720 trommel screen
b. University of California, Riverside, Department of Environmental Sciences, Contact: Dr.
David Crohn, E-mail: firstname.lastname@example.org
• The addition of rockwool to green waste during the composting process did not have
any negative impacts.
• In all cases, the addition of rockwool had no significant effect on either germination or
• Used rockwool can be safely mixed with green waste feedstock at low volumes and can
• Process: Open windrow. Equipment used: medium sized commercial tub grinder
(Morbark Model 1100) and further screened to 3/4" fines
CHA would like for people to comment on this article and share how they feel regarding these practices. Only when we come together as a community, can we decide how to impact large industries disrupting the ecosystems and our health. Based on the current breadth of knowledge regarding rockwool, it is advisable to begin seeking alternative solutions, like coco base hydroponic media and the bark based cloning media or soil based cloning techniques. We will begin to cover these topics more in depth as time goes on, like the sustainability of peat and the binding agents in the other plugs, but for now, hopefully a few eyebrows have been raised as the butterfly continues to flap its wings…
Want to try something other than rockwool? Give these Root Riot or iHort plugs a test drive….