The IUCN/SSC Shark Specialist Group
Shark News 5: October 1995
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Cyanide Spill in the Essequibo River, Guyana
Regrettably fulfilling one of the predictions made by Compagno and
Cook (1995), the Essequibo, Guyana's largest river, was affected in
August by a major cyanide waste spill. More than 325 million gallons
of the toxic chemical were reported in Earthweek (Chronical Press) to
have escaped from a gold mine operated by US and Canadian
companies. Large numbers of fish, mammals and birds were killed
and public drinking water supplies threatened as the spill flowed
50 miles downstream. International relief teams rushed to divert the
cyanide into a holding pond near the mines, which use the chemical
to extract gold.
Species potentially affected by this spill may have included the
bull shark Carcharhinus leucas, largetooth sawfish Pristis perotteti,
and smoothback river stingray Potamotrygon orbignyi. The stingray
is well-recorded from the Essequibo as part of a wider distribution that
includes Venezuela, Guyana, French Guiana, Suriname, the
Columbian and Brazilian Amazon and Para River drainages.
Cyanide and related cyanogen glycosides are listed as
"supertoxic" compounds by Turkington (1994). Fewer than seven
drops of most liquid forms can kill a 68 kg (150 lb) man in less than
15 minutes, depending upon factors that alter rate of absorption.
Cyanides act through interference with enzyme activity at oxygen
sites in haemoglobin of red blood cells and myoglobin in muscle
tissue for vertebrates, and the counterpart oxygen-carrying porphyrins
for invertebrates (haemocyanin etc.). Binding of sites is regarded as
irreversible, with death depending on how much oxygen deprivation
occurs as a percentage of total innate oxygen-carrying capacity for
given porphyrins and animal size. Small animals are considered to be
disproportionately susceptible to fatality at lower ambient cyanide
levels.
References
Compagno, L.J.V., and S.F. Cook. 1995. The exploitation and
conservation of freshwater elasmobranchs: status of taxa and
prospects for the future. In: Volume VII -The biology of freshwater
elasmobranchs (ed. Oetinger & Zorzi). Journal of Aquariculture and
Aquatic Sciences, VII: 62-90.
Compagno, L.J.V., and S.F. Cook. 1995. Freshwater elasmobranchs:
a questionable future. Shark News 3: 4-6.
Turkington, C. 1994. Poisons and antidotes: everything you need to
know. Facts on File Press. New York. 372 pp.
Sid Cook
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