My brushes are very environmentally friendly.
Bamboo is one of the more renewable plants. Most of my bamboo comes to me by way of Craigslist ads i place where i offer to clean up bamboo growing around a house. Usually the bamboo has not been touched in years. The owner of the bamboo gets their bamboo cleaned out and transformed into a work of living art. I get a trailer full of bamboo and often a sore back.
My more exotic brush bristle materials were at one time a small part of someone else’s trophy. I find some of the materials by way of estate sales where i buy a hide, a shawl or similar, and transform it into many high quality, and one of a kind brushes. This is known as up-cycling or re-purposing.
Some of the bristle material i use, such as goat, pony, and sabeline hair, as examples, are collected by way of giving the the animals a hair cut. As an aside, the goat hair i use is carefully cleaned and prepared for use as makeup brushes. No harm comes to the goats, ponies or Oxen, beyond receiving a haircut. The hair is always cleaned before and after becoming paintbrushes, and the material is completely renewable.
My manufacturing is also environmentally friendly. Bamboo dust from cutting and sanding is the biggest byproduct and all of it recycled. I use the saw and sanding dust as lawn fertilizer.
I also use synthetic filaments for some brushes, which i like to joke come from Unicorns who visit my studio in the Spring and let me comb out their winter coats.
My synthetic filaments are designed to last up to about 20 years with reasonable care and most types of natural hair can last up to hundreds of years, again with reasonable care. Natural hair can last up to many thousands of years if protected.