<Tr> <Td> Fire diamond for copper metal </Td> </Tr> <P> Gram quantities of various copper salts have been taken in suicide attempts and produced acute copper toxicity in humans, possibly due to redox cycling and the generation of reactive oxygen species that damage DNA . Corresponding amounts of copper salts (30 mg / kg) are toxic in animals . A minimum dietary value for healthy growth in rabbits has been reported to be at least 3 ppm in the diet . However, higher concentrations of copper (100 ppm, 200 ppm, or 500 ppm) in the diet of rabbits may favorably influence feed conversion efficiency, growth rates, and carcass dressing percentages . </P> <P> Chronic copper toxicity does not normally occur in humans because of transport systems that regulate absorption and excretion . Autosomal recessive mutations in copper transport proteins can disable these systems, leading to Wilson's disease with copper accumulation and cirrhosis of the liver in persons who have inherited two defective genes . </P> <P> Elevated copper levels have also been linked to worsening symptoms of Alzheimer's disease . </P>

Who discovered copper and when was it discovered