Scientists test different approaches to reduce copper in San Diego Bay
The U.S. Environmental Protection Agency (EPA) and state and local water quality boards across the U.S. have mandated that numerous bays and harbors reduce toxic copper levels in seawater by definitive specified dates. The presence of toxic copper is the result of copper leaching from copper-based paints on ocean-going vessels anchored in marinas. Toxic copper poisoning of the nation’s waterways is at epidemic proportions; it is estimated that more than 2,000 captive seawater sites in the U.S. alone have toxic copper levels. Mandates have resulted in responses focused on either moving the water, treating the boats and/or treating the water. All efforts have met with marginal success to date.
Copper enters the water column as total copper. It is derived from the hulls of boats, on which copper-based paints are used to discourage barnacle growth. For example, a 5-billion-gal bay may have 25,000 lb of new copper released annually. This is in addition to the levels of soluble copper already present in the water column. Usually, 0.05% of the total copper load appears as soluble toxic copper, the balance being absorbed directly by organic matter or by forming chelates that settle in the silt. So three factors contribute to the problem: current levels of toxic copper, new total copper load, and stirring up silt, which allows chelated copper to re-solubilize to the toxic form. Copper in seawater has a toxic effect on algae, mollusks and other crustaceans, and certain sea grasses, thus disrupting the food chain. Safety to humans is of minimal concern.
Toxic copper typically enters the water column at high parts per billion (ppb) levels, usually 8 to 10 ppb, and mandates specify a target level of less 3.1 ppb on a daily monitoring basis. To understand the magnitude of the problem facing bays and harbors, a typical small bay may contain more than 5 billion gal of contaminated water. Often bays and harbors have limited tidal action, so methods other than moving the water are required to meet federal and state mandates. Treating boats with copper-free paints has had a limited effect on overall copper reduction, as documented in numerous controlled studies, with most studies showing less than 4% reduction.
As of late, options for the remedial treatment of water have been limited by the availability of effective remedial processes for toxic copper removal from seawater; however, the implementation of specific target dates for soluble toxic copper reduction and the needed reduction of new levels of total copper yearly has fostered innovation in methods for the remediation of copper from the water column. There are several such approaches.
One such approach, by Red Lion Chem Tech, employs submersible ballasts containing adsorbent that actively addresses the soluble toxic copper problem in localized target areas in the water column. This approach is based on wave action, wherein seawater passes through the ballasts and toxic copper is permanently bound. The other approach, designed for removal of all forms of total copper on a larger and faster basis, involves pump-and-treat, wherein seawater is pumped at a high filtration rate through industrial-sized test bed columns for effective rapid reduction of total copper in a single pass.
Scientists have developed proprietary methods in coordination chemistry that is selective for copper in seawater and unaffected by other ions. Seawater is rich in divalent cations. In addition, a poly-combinatorial adsorbent approach has been developed by the company to address other EPA mandates for removal of other toxic substances in seawater, which include toxic heavy metals such as lead, mercury and arsenic; petrochemical seawater contaminants such as oil and grease, gasoline, diesel and the like; volatile organic compounds; semi-volatile organic compounds; PCBs; organochlorine pesticides; and chemicals defined as priority ocean pollutants in the Clean Water Act.
In a particular controlled laboratory study, Red Lion Chem Tech scientists demonstrated the ability to remove 95% of copper from seawater in a single treatment by either method, ballast or pump-and-treat, and are now conducting field trials in mandated areas in Southern California. To demonstrate feasibility, six seawater samples were collected from EPA-mandated and non-mandated areas in the San Diego Bay. Samples were collected under full chain of custody and transported to Red Lion Chem Tech for testing. Seawater testing was performed by two methods: ballast treatment for 96 hours and pump-and-treat for less than one minute. The latter process only was utilized on the fifth and sixth samples. Samples of seawater were collected both before and after treatment and submitted to an independent certified laboratory for testing. Testing was done according to EPA Method 1640 for total copper.
Results from treatment of samples by ballasts for 96 hours are shown in Figure 1, wherein an average of 94.6% reduction in seawater copper levels was observed following a single treatment with the flow-through ballast for 96 hours with a reduction from 10 ppb to 0.45 ppb for the highest sample, Sample 1, taken from the impacted area.
Results from the pump-and-treat column filtration system with samples 5 and 6 showed a comparable reduction of copper in seawater of 94.85%, compared with the flow-through ballast system of 94.6%. The difference between the two methods is not statistically significant. The major observation, however, is the time of treatment: the flow-through ballast required 96 hours for reduction; whereas the pump-and-treat column filtration method was complete in less than one minute under pressure conditions.
Scientists continue to test both approaches in mandated waters in Southern California. If successful, the two methodologies will be applied to other impacted waters in California and other regions of the U.S. Also under development are large tarps containing adsorbent for use in hull cleaning. The highest load of new copper load occurs at the time of hull cleaning in marinas. It is hopeful that remedial treatment of impacted waters with these new methodologies will allow affected bays and harbors to hit their mandated cleanup dates when implemented as part of an overall best practice plan to reduce toxic and total copper contamination of seawater.