Interesting patterns, however, it is notable that all of the natural scenes of green probably contained high levels of arsenic - as that was one of the key ingredients in green coloring during Victorian times.
The article does say, "All these papers, and nearly all that Morris then went on to design were printed using hand-cut woodblocks loaded with natural, mineral-based dyes." Is arsenic classed as a natural, mineral-based dye?
I'd say yes: Arsenic is present in dyes classified as natural, mineral-based, according to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315675/ ("Natural Colorants: Historical, Processing and Sustainable Prospects").
https://www.youtube.com/watch?v=MvxnXOoFl20