The correct option is C
$$1, 2, 3, 4$$
1. Arsenic poisoning causes black foot disease as arsenic is a carcinogen that results in darkening of the skin and abdominal issues.
2. Secondary treatment to the effluents involves a biological process in which the organic matter in the effluent is decomposed by the bacteria and fungi.
3. Pyrolysis is the process in which the solid soil is subjected to the high temperature to decompose it into ash.
4. Tubifex is a roundworm that can sustain the polluted water that has low levels of dissolved oxygen and heavy metal deposition. So, its growth in any water body indicates water pollution.
5. Biomagnification is the ability of the non-degradable pollutants to stay in the adipose tissues of the living organisms and persist in higher concentration.
Hence, the correct answer is '1,2,3,4'.