Report Number: 123
Year: 2008

Heavy Metals in Biotic Representatives from the Intertidal Zone and Nearshore Waters of Tanapag Lagoon, Saipan, Commonwealth of the Northern Mariana Islands (CNMI)

Tanapag Lagoon borders the western shore of central Saipan. It harbors a rich diversity of marine life and supports a variety of commercial and recreational activities. Over the last quarter century, Tanapag Lagoon has become heavily impacted by the activities of man. Primary sources of anthropogenic disturbance in these waters include a power station and commercial port (Saipan Harbor), two small boat marinas, a sewer outfall, several garment factories, auto and boat repair shops, wood shops, government vehicle maintenance yards, a commercial laundry, and an acetylene gas producer. There are also a number of old military dumps and disposal sites in the area as well as a municipal dump that served as the island's only solid waste disposal site for over 50 years before its gates were permanently closed in February, 2003. Several streams and storm drains empty into the lagoon during the rainy season and provide a mode of transport into the ocean for any land-based contaminants. Overflows from sewer lines are also commonplace at this time of the year and the whole area is inundated by storm water runoff during periods of prolonged wet weather. The effects of these perturbations on the indigenous biota within the lagoon are largely unknown.Likewise, fundamental data describing the abundance and distribution of persistent and potentially toxic pollutants within the system is also lacking. Mindful of these shortcomings, a contaminant assessment of surface sediments within Tanapag Lagoon was completed in 2001 and identified significant metal enrichment in the southern half of the lagoon, particularly around the dump. The study described herein examined trace metal levels in biotic components within the lagoon and was seen as a logical extension of the work already completed. Sampling was conducted in June 2003 and focused on a suit of dominant ecological representatives (algae, seagrass, seacucumbers, bivalves and juvenile fish) and intertidal sediments collected from 12 sites along the coast between Micro Beach (Garapan), at the southern end of the lagoon, and Pau Pau Beach Park (San Roque) in the north. These representatives included species with known or suspected bioindicator potential as well as those popularly harvested for human consumption.

The study confirmed previous findings of trace metal enrichment in surface sediments around the base of the Puerto Rico Dump. Levels of copper, lead and zinc measured here were at least two orders of magnitude higher than the lowest values determined elsewhere in the lagoon, while values for cadmium, chromium, mercury and nickel were at least one order of magnitude higher. It also clearly demonstrated that this enrichment is being transmitted to biotic components in the area although the implications from the data are that natural processes operating in the sediments and overlying water column place some constraints on rates of transfer. Significant copper, lead and zinc enrichment was identified at Echo Bay, Seaplane Ramps and CUC Beach. Overall the findings reflected inter-specific differences in bioindicator capabilities of the organisms analyzed as well as inter-site differences in the sources, abundances and biological availabilities of trace metals in the sediments and overlying water column. All bivalves collected close to the dump exceeded the current US FDA non enforceable guidelines for Pb in shellfish, and several international standards for Cu in fish and fisheries products. Trace metal levels in the edible tissues of all other organisms sampled within the lagoon were all well below critical threshold levels of concern

Gary R. W. Denton
Brian G. Bearden
Peter Houk
J. A. Starmer