Many heavy metals such as iron, gold, and silver have essentially no deleterious effect on human cells;
cadmium, lead, and mercury, however, are extremely harmful because even a trace amount can bioaccumulate in the body – specifically the lungs, kidneys, or liver – and impede metabolic functions.a) cadmium, lead, and mercury, however, are extremely harmful because even a trace amount can bioaccumulate in the body – specifically the lungs, kidneys, or liver – and impede metabolic functions - Correct. Parallelism is maintained.
b) however, even a trace amount of cadmium, lead, and mercury can bioaccumulate in the body – specifically the lungs, kidneys, and liver – and impede metabolic functions making them extremely harmful - non-underlined portion clearly suggests that next sentence shall begin with metals and not trace amount. Change in meaning due to replacement of words. Them is ambiguous - Which it refers to 'cadmium, lead, and mercury' or 'metabolic functions' ?
c) cadmium, lead, and mercury, however, are extremely harmful because even a trace amount can bioaccumulate in the body – specifically the lungs, kidneys, and liver – and cause metabolic functions to be impeded by them - Passive construction. Wordy. Them is ambiguous.
d) however, because even a trace amount of cadmium, lead, and mercury can bioaccumulate in the body, lungs, kidneys, or liver, and impede metabolic functions, they are extremely harmful - non-underlined portion clearly suggests that next sentence shall begin with metals and not trace amount. ''lungs, kidneys, or liver'' are further specification to Body and not in parallel with it. They is ambiguous. Replacement of words changes the meaning.
e) however, cadmium, lead, and mercury have a trace amount that can bioaccumulate in the body, specifically in the lungs, kidneys, or liver, impeding metabolic functions and causing extreme harm - 'impeding' and 'causing' are not effect of main verb 'have a trace amount that can.......'
However more explanation is desired....