Abstract

The concentrations of aluminum were analyzed for sediment samples taken from ten sites in the Puget Sound region of Washington state. Samples were collected from shoreline, inter-tidal sub-tidal zones. Concentrations of aluminum were higher in the collection range (San Juan Island region, while lower concentrations were found in the Southern range which included Elliott Bay in Seattle and Des Moines Beach Park in Des Moines, Washington. No significant relationships were found between aluminum concentrations and grain size.

Introduction

Aluminum is the most abundant naturally occurring metal, the third most common element, and composes approximately 8% of the earth's crust (Boegman and Bates 1984). it is an essential constituent of most important rocks except the peridotiles sandstone and limestone. It is oxidized very easily and therefore does not occur in native form. In nature it exists as a trivalent metal. Aluminum is found primarily in silicates such as feldspars, micas and clays and is also found in the oxide, or bauxite form.

It has long been thought that aluminum played an innocuous role in the environment. However, with the advent of increasing industrial pollution and acid rain, aluminum is assuming a more role in environmental health assessment. The neurotoxicity is particularly important in geographical areas where high levels of aluminum salts are present in the soil (Perl et al. 1982) or can be leached out by acid rain resulting from atmospheric pollutants.

In Puget Sound, aluminum has been found to play an important role in sediments as a "sink" for certain forms of industrial pollution. Crecelius et al. (1975) have shown that in "non-contaminated" muds of Puget Sound, the majority of arsenic and half the antimony appear to be bound to the extractable. It appears that the majority of arsenic and antimony are bound to the sediments, in some manner other than the readily oxidizable organic matter. Other researchers have shown that some soils high in reactive amphorous iron and aluminum compounds absorb large amounts of arsenic, (Jacobs et al. 1970 and Woolson et al. 1971).

In a necropsy on a Gray whale (Eschrichtirobustusus robustus) found near Port Angeles, Washington, (Malins et al. 1983) reported finding high levels of aluminum in the blood and brain tissue residues. The lowest concentration of aluminum found in brain tissue was 2.2 parts per million wet weight, while that of the whole blood averaged 2.2 ppm- In studies with laboratory animals (Marguis 1982) and humans (Crapper McLachlan et al. 1983) correlations were established between aluminum body burdens, behavioral changes and serious neurological damage that may result in death.

The Gray whale is a unique animal in several respects, but of particular importance are its feeding habits. Gray whales are exclusively bottom feeders (Minasian et al. 1984) and gain most of their nutrition from crustaceans and a wide variety of other invertebrates that inhabit sediments in the ocean floor. To that end, Gray whales are terrific bio-accumulators.

During seasonal migrations, Gray whales frequent the coastal areas of Washington and often feed in Puget Sound. This may be of great importance as any direct industrial and non-industrial pollutants that accumulate in the sediments will be ingested by feeding whales. As a result, toxicological studies on stranded and deceased Gray whales may play a vital role as an environmental indicator. Unfortunately such studies are virtually non-existent, thus direct studies focusing on the sediments themselves are of utmost importance, for in a biologically productive area such as Puget Sound, the sediments play a tremendous role as a link in the food chain.

Collection and Analytical Procedures

Sediment samples were divided into three categories; sub-tidal, inter-tidal (<1 meter in depth) and shoreline (above high tide). The sub-tidal samples were collected with a 0.3 meter Van Veen Grab. The procedure for sampling followed the Puget Sound Estuary Protocol (10-13) manual. Inter-tidal and shoreline samples were obtained using a two square meter grid with sediments being collected at each corner of the grid. The grid was then flipped end-over-end with sediments collected at the next interval. This method insured that samples were collected in a uniform manner.

Upon collection the sediments were placed in clean polypropylene or polystyrene sample containers and coded with location, depth, weather conditions and sediment texture. Field blanks were prepared and transported to and from each site. All samples were kept in a cooler while in the field and refrigerated within seven hours.

Locations of sub-tital sediments were measured with a Loran nevigation system (Table 1).

Table 1. Locations of Sub-tidal Sediments Site Latitude/Longitude Time

Precise locations for inter-tidal and shoreline sites were obtained from navigational reference maps (Table 2).

Table 2. Locations of Inter-tidal and Shoreline Collection Sites.

While a variety of methods for sediment digestion were researched, the one selected came from the Puget Sound Estuary Protocol Manual (B27-B29). There are several reasons why this method was chosen. The metals protocol is an approach involving federal, state and local institutions and describes standard chemical tests and standardized interpretation guidelines for use by all Puget Sound regulatory agencies concerned with sediment contamination. This is of great importance if any data replication is to be established.

There were several modifications to the Puget Sound Protocols. These procedures are geared to digest a large quantity of samples over a short period of time. The procedure used was set up to digest a small quantity with more controlled and complete digestion using Kjeldahl methods. Flame atomic absorption analysis with acetylene and nitrous oxide as the oxidant was employed using a Perkin-Elmer model 370 atomic82 absorption spectrophotometer with direct aspiration. Concentrations of aluminum were recorded and converted (Figure 1) to reporting levels in dry weight (mg/kg). For each site,

Figure 1. Equation for converting concentration of aluminum to dry weight.

Individual samples were averaged to be site specific. Fitness of data was tested for using a Q-factor analysis (Christianson 1980). Population standard deviations (Table 3) were calculated and reported for each site.

Table 3. Population Standard Deviation and Q-Factor Coefficient

Data

The concentration of aluminum and suporting information on location, water depth and sediment type, are listed in Table 4.

Due to the limited nature of the study and the amount of data available, it was not feasible or possible to construct a correlation coefficient matrix.

Standard sieve techniques were used for grain sized analysis. Samples containing a majority of material larger than 62 micrometers and less than 2 millimeters were classified as sand (Crecelius et al. 1974).

Table 4. Concentrations of aluminum in sediments of Puget Sound

The digestion and analysis of the crab and sea! tissues were done in a random manner to determine the most effective methodology and were not statistically analyzed.

Results and Discussion

The concentration of aluminum in Puget Sound sediments ranged from 50.4ppm -86.6ppm (0.76% - 1.35%) for inter-tidal samples 63.4ppm - 75.4ppm (1.16% - 2.15%) for sub-tidal samples and 43.1ppm 97.1ppm (0.71% - 1.85%) for shoreline samples.

For the inter-tidal samples the lowest concentrations were found near Anacortes, Washington. These sediments had a very coarse gravel substrate with virtually no clays or sand and could be expected to show lesser concentrations as peridotiles and limestones have lower aluminum contents. The highest concentration of aluminum from this zone was found in gravel substrate.

The sub-tidal samples were collected near Rosario Strait near Guemes and Cypress Islands in the San Juan islands. Lowest concentrations of aluminum were found at site E. sites D and F much higher levels even though they were in the same vicinity.

Samples from site E contained high amounts of organic matter that would have affected the overall percent solids determination. This may not affect the concentration from the wet weight, but would give an erroneous value for the dry weight and percent concentrations. This is somewhat supported by the high value obtained for the standard deviation. A Q - factor analysis performed on site E and all data were deemed fit for analysis.

For shoreline samples, sediments collected at Alki Point (AP) showed the lowest levels of aluminum while samples taken from the Green River (GR) showed the highest.

Collectively sediments from the sub-tidal Zones showed a considerably higher concentration of aluminum than those collected from other areas. Aluminum found in Puget Sound are mainly bound up in silicate matrices. One might assume that concentrations of aluminum would be uniform throughout the surface sediments, but this is not evident. Not all matrix-bound aluminum exists in the silicate, form. Industrially generated aluminum oxide residues are released into the water. Some of the aluminum in these residues becomes available upon digestion with strong acids, and may increase the levels for the naturally occurring aluminum. This may account For the higher values obtained for D, E and F.

Crecelius et al. (1975) found a significant correlation between sediment grain size and levels of aluminum. Their findings stated that finer-grained sediments contained less aluminum than coarser-grained sediments. Though no statistical matrices were performed in our study, no qualitative correlations were seen to exist. The general trend shows higher levels in the Northern part of the collection range and lower levels in the Southern.

Given the detrimental effects of aluminum in biological systems, a continuing analysis of sediment concentrations of this and other metals should be implemented. This undertaking of aluminum analysis in Puget Sound is preliminary in nature and warrants continued study.

Acknowledgements

I would like to thank Dr. Herb Brice for his input and approval of this project, Seattle Central Community College for the use of its facilities, Dr. Tag Gornall for all his advice and insight, and Jeffrey Rash for all his help, humor, and manual labor. I would like to thank the staff at Metro Environmental Laboratories for their analytical help and reference materials, Dr. Lee Monteith of the University of Washington and Gordy Uno for working together to learn more about the role of aluminum in our environment.

References

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2.  Christian, S.D., Analytical Chemistry, 3rd edition, New York: John Wiley and Sons, Inc., p. 80, pp. 78-79.

3.  Crapper Mclachalan, D.R., Farrel, B., Galin, H., Karlik, S., Eichhorn, G., and Deboni, U. 1983. Aluminum in Human Brain Disease, in: Biological Aspects of Metals and Metal Related Disease. (B. Sarker, ed.) Raven Press NY.

4.  Crecelius, E.A., Bothner, M.H., Carpenter, R., Geochemistries of Arsenic, Antimony, Mercury and Related Elements in Sediments of Puget Sound. Current Research. 1975. vo 325-333, University of Washington, Seattle. WA 98195.

5.  Jacob, L.W. Syers, J.K., Keeney, D.R., Soil Sci. Soc. Amer. Proc. 34, 750-4 (1970).

6.  Malins, D.C., Brown, D.W. Chan, S., Chemical Analysis of Samples from a Deceased Gray Whale, unpublished, Northwest and Alaska Fisheries Center, Environmental Conservation Division, Seattle, WA 98112 (1984).

7.  Marquis, J.K. 1982. Aluminum Neurotoxicity, An Experimental Perspective. Bull. Environ. Contam.Toxicol.

8.  19: 43-49.

9.  Minasian, S.M., Balcomb, III, K.C. Foster. L., The World's Whales. pp 62-63, Smithsonian Books (1984) Washington D.C.

10. Puget Sound Estuary Program, Recommended Protocols for Measuring Metals in Puget Sound Water, Sediment and Tissue Samples 1986. pp 1-27, A1-B6, Tetra-Tech Inc., Bellevue, WA 98005.

11. Woolson, E.A. Axley, J.H. Kearney, P.C., Ibid., 35, 101-5 (1971).