Many leaf vegetables become less edible as they age and bitter, or potentially even toxic, compounds start to form.
[3][4] Since most leaf vegetables are very difficult to store and keep well, commercial production and distribution requires a high amount of pollution and plastic waste.
Plants growing in soils contaminated with heavy metals or pesticides can accumulate those pollutants (at different proclivities for different species).
[5] In addition, the misidentification of species may often lead to consumption of poisonous and toxic plants.
[6] This can generally be mitigated by a familiarity with the plants of one’s region, specifically the desired vegetable, and any lookalikes.