National Fisheries Laboratory Division, Bureau of Fisheries and Aquatic Resource, Quezon City, Philippines
Illegal cyanide fishing is practiced by some fishers to capture agile and otherwise inaccessible reef fishes easily. Economic incentives had prevented discontinuation of the practice despite regulations present. Aside from the well-known toxicity of cyanide, it is a concern whether the fish is for ornamental purposes or human consumption that cyanide is being used because of the environmental damage it can cause by killing off non-target species. Currently, the cyanide content of fish is determined using an ion-selective electrode (ISE), with distillation as the mode of extraction of cyanide from tissues. This paper reports a modification of ASTM Method 500-CN-E, a method originally used to test for cyanide content in the wastewater. This paper outlines the process of determining the applicability of the method modification for analysis of fish tissue samples, in which no standard method was designed specifically for the matrix mentioned above. Although percent recoveries for cyanide at 0.05-10 mg/L range in spiked distilled water matrices are in line with the American Society of Testing and Materials (ASTM) results (90-105%), cyanide recoveries in spiked fish tissue matrices at the same concentration range are appreciably lower (~60-80%). For regulatory purposes, it serves as a temporarily acceptable method to detect cyanide-laden fish until a suitable method can be validated on international standards. However, to be accepted as a standard method, additional modifications may be needed or proven in inter-laboratory tests that the recovery of cyanide in fish is consistently low.