Heavy metal.
Chromium is an environmental contaminant usually released into waters by metallurgical, tanning and other industries. (ref. ID; 4497)
Tanneries and electroplanting industries are the major sources of hexavalent chromium pollution. Metal finishing industries, coal combustion byproduct in thermal power plant and application of sewage for agricultural purposes. (ref. ID; 6725)

[Cr: an atomic absorption standard solution 1,000 ug Cr per ml (nominal) in 1% HNO3]
Test organisms;
Rotifera: Lecane hamata (ref. ID; 6861)
Rotifera: Lecane luna (ref. ID; 6861)
Rotifera: Lecane quadridentata (ref. ID; 6861)

[Ammonium Dichromate] CAS[7789-09-5] UN1439
Chemical formula; (NH4)2CrO7
Test organisms;
Oligochaeta: Tubifex tubifex (ref. ID; 1318)

[Chromium(III) Nitrate]
Chemical formula;
Test organisms;
Oligochaeta: Eisenia andrei (ref. ID; 6831)
Nematoda: Caenorhabditis elegans (ref. ID; 6823)

[Chromium(VI) Trioxide] CAS[1333-82-0]
Chemical formula; CrO3
Test organisms;
Protozoa: Euglena gracilis var. bacillaris (ref. ID; 3896)
Oligochaeta: Tubifex tubifex (ref. ID; 1318)

[Potassium Chromate] CAS[7789-00-6] UN3288
Chemical formula; K2CrO4
Test organisms;
Protozoa: Colpidium campylum (ref. ID; 6081)

[Potassium(VI) Dichromate] CAS[7778-50-9] UN3087
Chemical formula; K2Cr2O7
Chemical characteristics; water soluble
Mode of action; Cr(IV) produces reactive oxygen species (ROS) in the cellular system, which can be a major cause of DNA damage. (ref. ID; 6725)
Test organisms;
Protozoa: Euglena gracilis (ref. ID; 3312, 4497)
Protozoa: Colpidium campylum (ref. ID; 6081)
Protozoa: Spirostomum teres (ref. ID; 6838)
Protozoa: Vorticella microstoma (ref. ID; 4989)
Protozoa: Activated sludge protozoan community (ref. ID; 6006)
Oligochaeta: Dichogaster curgensis (ref. ID; 6725)
Oligochaeta: Eisenia foetida (ref. ID; 6001)
Oligochaeta: Enchytraeus albidus (ref. ID; 5909)
Oligochaeta: Tubifex tubifex (ref. ID; 6079, 6080, 6636, 6968)
Nematoda: Caenorhabditis elegans (ref. ID; 506, 6824)

[Tannery effluents]
Test organisms;
Oligochaeta: Lampito mauritii (ref. ID; 6008)