Excerpts from Jim Conrad's
from the May 4, 2014 Newsletter issued from the Frio Canyon Nature Education
Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
ZINC ON THE ROOF
Neighbor Phred pointed out something interesting on the roof of the building I was painting. That's it below:
The slanting roof below the old galvanized-steel ventilator is lighter than the surrounding roof area. Phred said that zinc bled from the ventilator metal, killing moss growing on and darkening the roof. When we looked around at other roofs in the area, similar effects were seen. I figured that in our arid climate maybe the roof darkening was more likely caused by lichen and cyanobacteria than moss, but otherwise it was clear that something was bleaching the roof below the ventilator.
It turns out that a sizable industry is practiced by folks eager for a good fee to nail "zinc strips" on roofs in order to keep the roofs from darkening from the growth of "moss, algae and lichens." Moreover, many of the industry's websites show pictures like ours, and some pictures definitely portray moss communities being impacted, such as one on an Oregon State University page at http://bryophytes.science.oregonstate.edu/page24.htm.
That page claims that zinc strips and galvanized flashing are apparently relatively safe and inexpensive ways to "... effectively kill or retard the growth of mosses and fungi and appear to have effect up to 15 feet below the zinc flashing along the length of the flashing." Most brands of zinc strips are effective for about a year, while the effects of galvanized flashing can persist for decades.
In school we learn that zinc is an essential nutrient for living things. In human bodies, zinc is the second most abundant trace mineral after iron, and is known to be a key mineral for cell and tissue renewal. It's also important for blood clotting, sperm production and the formation of testosterone. It acts as an antioxidant, and helps to maintain proper vision and a normal sense of taste and smell.
However, in humans, too much zinc can result in conditions known as the "zinc shakes" or "zinc chills," involving nausea, vomiting, cramps and diarrhea. People have died from exposure to zinc chloride fumes, and livestock have died from inhaling air contaminated with lead and zinc. I find no source describing a specific biochemical mechanism causing zinc toxicity, though one source says that zinc binds to proteins and organic acids in plants. Other studies find that a certain concentration of zinc might harm one moss species, but enhance growth in another.
So, with this mishmash of information in mind, now every time I see that roof with its ventilator and wiped-out biotic community, it sets off a whole series of thoughts.
For one thing, I wonder: If a simple roof ventilator can so decisively impact the ecology around it, what else around us might be affecting our health, including the way we think and feel? What are the deteriorating underground pipes carrying our water to us adding to our water, or the slowly dissolving plastic containers our store-bought water comes in? What about city air, and the chemicals governments spray us with to kill weeds, or keep down mosquitoes?
Also, I wonder: Who said that a roof darkened with moss or lichen is ugly or that the roof's natural biotic community needs to be destroyed? What's wrong with the notion that a roof growing dark with lichen and moss looks and feels more "homey," settled and at ease with the world around it? Who gets to establish the norms for social ethics and for esthetics in general?
Is this slightly off-kilter feeling I'm experiencing right now caused by my hypoglycemia, or the fillings in my teeth that have been eroding away since the 1960s and 1970s? Or the chemicals they used to flush the well dug here a while back, now with residues in my drinkwater?
Each time I see how that old roof ventilator has killed things around it, it gives me the creeps.