Report Number: 130
Year: 2010

Impact of Land-Based Sources of Pollution on Coastal Water Quality of Saipan, Commonwealth of the Northern Mariana Islands (CNMI): Arsenic, Mercury and PCBs in Popular Table Fish from Saipan Lagoon.

Popular table fish were taken from 11 sites in the northern half of Saipan Lagoon and analyzed for total arsenic, total mercury and 20 PCB congeners, as part of an ongoing pollution monitoring and assessment program for Saipan’s coastal waters. In all, 340 specimens representing 67 different species from four different trophic levels (20 herbivores, 7 planktivores, 5 omnivores and 35 carnivores) were collected between October 2004 and January 2005. Arsenic and mercury levels were determined in the axial muscle of all 340 representatives and in the hepatic tissues of 259 of them. PCB analysis was conducted only on axial muscle of 324 specimens.

Total arsenic levels in muscle and liver tissues range from 0.03-36.2 µg/g and 0.07-104 µg/g wet weight respectively. The majority of tissue samples analyzed yielded values of less than 5 µg/g wet weight. While no obvious site-dependant difference in arsenic availability emerged from the data, there were clear trophic level-dependant differences with herbivores generally containing the lowest concentrations. The planktiverous genera, Myripristis, were particularly noteworthy accumulators of this element. Other representatives with a propensity for arsenic included Parupeneus multifasciatus (multi-barred goatfish), Neoniphon opercularis (black-finned squirrelfish), Thalassoma trilobatum (Christmas wrasse) and Rhinecanthus spp. (trigger fish).

Total mercury concentrations in muscle and liver tissues ranged from 0.001-0.616 µg/g wet weight and 0.004-9.931 µg/g weight respectively. Levels in the former tissues were less than 0.10 µg/g in over 80% of fish analyzed. In the latter tissue, levels were less than 0.20 µg/g in approximately the same percentage. Inter-site data comparisons revealed a clear north to south increase in mercury availability with the highest levels generally occurring in fish from the Hafa Adai Beach area (Site 9). Despite some considerable variability within trophic levels, the data strongly supported the concept of mercury biomagnification with the overall average value in carnivores exceeding that in herbivores by approximately one order of magnitude.

Σ20PCB levels in fish axial muscle tissue ranged from 0.04-145 ng/g dry weight with close to 90% of all fish analyzed yielding values of less than 20 ng/g. Wet weight approximations were computed from the raw data assuming muscle to be 77% water. Total PCBs levels in fish muscle were estimated by doubling Σ20PCB concentrations. No obvious site- or trophic level-dependant differences emerged from the data. PCBs 101, 118 and 153 were the most frequently encountered congeners and were detected in over 80% of samples analyzed. They also ranked among the most abundant congeners, accounting for 8-28% of Σ20PCBs on average. While the more toxic coplanar chlorobiphenyls, PCB 77 and PCB 126, were detected in 33% and 15% of all samples respectively, they had a collective average abundance of only 3.1%.

The toxicological significance of the data is discussed from a human health stand-point in light of national and international food standards and fish consumption advisories. For this purpose, total mercury and arsenic values determined in each fish were assumed to represent 100% and 1% of methylmercury and inorganic arsenic concentrations respectively. Total PCB approximations were obtained by doubling the Σ20PCB values. It was concluded that fish from the northern half of Saipan Lagoon contained inorganic arsenic and PCBs in their edible tissue at levels below toxicological thresholds of concern, and could be eaten on an unrestricted basis. In contrast, methylmercury levels in carnivorous species from the more southerly sites visited were generally above those considered acceptable for unrestricted fish consumption.

Gary R. W. Denton
Michael S. Trianni
Michael C. Tenorio