Mercury in tissues of mussel off southern California

Volume7/Number8/August 1976

Mercury in Tissues of Mussel off Southern California Total mercury content has been determined in three tissues of the intertidal mussel Mytilus californianus collected at locations along the southern California coast and at island control stations. The apparent influence of certain harbours and municipal wastewater outfalis was reflected by the relatively higher levels o f mercury in all tissues of mussels from these areas. In general, the concentrations reported here are lower than those in mussels on west European coasts.

of Southern California was conducted, the discharge of municipal wastewaters was found to be the predominant input route. Young et al. (1975) have estimated that approximately four metric tons of anthropogenic mercury now reside in the surface sediments off Palos Verdes Peninsula as a result of wastewaters discharged by the Los Angeles County Sanitation Districts near Royal Palms Beach (Sm. 9, Fig. 1). Mercury levels in these sediments typically range from 0.05 mg/kg (dry wt) in deep sediments to 5.0 mg/kg (dry wt) in the top 4 cm. However, data on the concentrations of mercury in tissues of the indigenous marine life remain scarce. Consequently, during 1974 we collected samples of the intertidal mussel, Mytilus californianus, from 14 coastal and 5 island stations in the Southern California Bight (Fig. 1). Several samples were obtained near submarine wastewater outfalls and harbours, known sources of heavy metals to the marine ecosystem; the island stations were used as control sites. Three tissues of these specimens were isolated and subsequently analysed for total mercury content.

Intertidal mussels provide an effective trapping mechanism for particulate matter present in nearshore waters. One advantage of this behaviour is that mussels can be used as indicators of marine pollution, a suggestion that has recently been made by several authors (DiSalvo etal., 1975; Goldberg, 1975; Alexander & Young, 1976). In locations such as the west European coasts (de Wolf, 1975) and the Southern California Bight, these organisms have proven sensitive to local variations in heavy metal levels that sometimes result from point source discharge of wastes. In the case of mercury, Klein & Goldberg (1970) drew attention to the potential impact of human activities on marine biota after finding enhanced levels of mercury in sediments near wastewater outfalls. Their observations have subsequently been confirmed (Young, 1974; Eganhouse et al., 1976) and when an analysis of the sources and distribution of mercury to the coastal waters

Sampling and Analysis

Specimens 3.5-6.5 cm in length were collected from the locations designated in Fig. 1; also shown axe locations of four major submarine discharges of municipal waste-

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Marine Pollution Bulletin TABLE 1 Mercury content (mg/kg wet wt) in tissues of mussels from Emma Woods State Beach (Stn. 4).

Total mercury No. of samples

Mean

Std. deviation

Range

Digestive gland

7

0.022

0.005

0.017-0.032

Adductor muscle

9

0.012

0.005

0.008-0.021

Gonads

8

0.005

0.002

0.002-0.010

Tissue

Results and Discussion

water in Southern California. All mussels were frozen until just before dissection, at which time composite samples of digestive gland, adductor muscle, and gonads were prepared from three specimens per collection. The total mercury content of the tissues was determined by a wet digestion, flarneless atomic absorption technique describedindetail elsewhere (Eganhouse, 1975). Recovery of mercury was tested by spiking samples of fish muscle with various quantities of mercuric chloride and methylmercuric chloride. The recoveries so obtained ranged from 95 to 106%. The accuracy of the technique was evaluated by analysing National Bureau of Standards reference material 1578 (tuna homogenate). We found this material to contain 0.99 ___0.04 mg Hg/kg (wet wt), in good agreement with the uncertified NBS value of 0.95 _+0.05 mg/kg (wet wt). An additional experiment was performed to determine the variability in mercury levels of mussels collected at one location. For this study ten composite samples were prepared from specimens collected at Stn. 4; the results are shown in Table I. The levels of mercury in digestive gland appear to be significantly less variable than those in the other tissues analysed. Thus, digestive gland analyses may provide a more reliable basis for evaluating relative environmental metal levels than data obtained for 'total soft parts' or other isolated tissues such as gonads or adductor muscle. It should be noted, however, that since individual tissues other than digestive gland may be more

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146

easily separated from associated sediments, such tissues as gonads or muscle may more clearly indicate the extent of physiological uptake than do digestive gland or whole soft tissue samples.

For ease of comparison the results for all three tissues have been plotted in Fig. 2. In this graph the abscissa does not correspond to distance but is used to show fluctuations found at stations along the coast. Inspection of these data reveals a markedly similar pattern for each of the three tissues, characterized by several distinct peaks. The highest levels of mercury were obtained for mussels found in Santa Barbara Harbour, (Stn. 3), just outside Oxnard Harbour (Stn. 5), in Santa Monica Bay (Stn. 7), on Palos Verdes Peninsula (Stn. 8 & 9), on Point Loma in San Diego (Stn. 14). The elevated levels observed near the Santa Barbara and Oxnard Harbours are probably associated with vessel activities (e.g. sediment deposits of mercury-bearing antifouling paints). There are no large discharges of municipal or industrial wastewater in these regions. Mussels collected off Santa MonicaPier (Stn. 7) exhibited a higher concentration of mercury in digestive gland than the island control samples, but this trend was not found for the two other tissues. The enhanced level in digestive gland may reflect some influence of the Hyperion Treatment Plant (M1), whose two municipal wastewater outfalls terminate at the head of Santa Monica Submarine Canyon. The high values in Palos Verdes and Point Loma specimens appear to be related to the submarine outfalls (M2 and M4) located in these areas. However, it is important to note that these regions contain two major commercial and naval harbours, San Pedro Harbou~ (just east of Palos Verdes Peninsula) and San Diego Harbour, which are known to contain mercury-contaminated sediments (Chen& Lu, 1974; EPA, 1974) and therefore constitute possible sources of mercury to the local biota. The digestive glands of the Royal Palms mussels (Stn. 9) contained 3.3 times the average levels of mercury found in the island samples. For adductor muscle and gonad tissues the ratios were 4.6 and 1.4, respectively. The ranges in values obtained for digestive gland, adductor muscle, and gonadal tissues were I 1 to 181 mg/kg, 7 to 88/zg/kg, and 5 to 32 mg/kg (all wet wt), respectively. These levels are much lower, in general, than those reported by de Wolf (1975) for Mytilus edulis and M. galloprovincialis collected from west European coasts. The differences may be due to physiological factors of the test organisms, systematic differences between analytical techniques, and/or differences in the pollutant loads of the environment. In summary, the usefulness of M. californianus as an indicator of mercury contamination off Southern California has been demonstrated. Highest concentrations were found in digestive gland; however, the levels were well below those reported for west European mussels. The authors wish to thank E. Motola for assistance in dissection, and M. Moore, M. Westbrook, and C. Patrickson for assistance in sampling.

Volume 7/Number 8/August 1976 R O B E R T P. E G A N H O U S E D A V I D R. Y O U N G Chemistry Section S o u t h e r n California C o a s t a l Water Research Project E l S e g u n d o , C A 90245, U S A

Alexander, G. V. & Young, D. R. (1976). Trace metals in southern California mussels. Mar. Pollut. BulL, 7, 7-9. Chert, K. Y. & Lu, J. C. S. (1974). Sediment Compositions in Los Angeles-Long Beach Harbors and San Pedro Basin. In Marine Studies of San Pedro Bay, California, Part 7 Sediment Investigations, ed. D. F. Soule and M. Oguri. Allan-HancockFoundation, University of Southern California, Los Angeles, CA. de Wolf, P. (1975). Mercury content of mussels from west European coasts. Mar. Pollut. BulL, 6, 61-3. DiSalvo, L. H., Guard, H. E. & Hunter, L. (1975). Tissue hydrocarbon burden of mussels as potential monitor of environmental hydrocarbon insult. Env. Sci. TechnoL, 9,247-52.

Eganhouse, R. P. (1975). The measurement of Total and Organic Mercury in Marine Sediments, Organisms, and Waters. TM 221, Southern California Coastal Water Research Project, E1 Segundo, California. Eganhouse, R. P., Johnson, J. N., Young, D. R. & McDermott, D. J. (1976). MercuD' in the Southern California Bight: Inputs, Distribution, and Fate. TM 227, Southern California Coastal Water Research Project, El Segundo, CA. EPA (1974). Draft Report to the San Diego Regional Water Quality Control Board on Guidelines for the Control of Shipyard Pollutants. Prepared by Environmental Protection Agency, National Field Investigations Center--Denver, CO. 1 July 1974. Goldberg, E. D. (1975). The musselwatch--a first step in global marine monitoring. Mar. Pollut. BulL,6, 111. Klein, D. H. & Goldberg, E. D. (1970). Mercury in the marine environment. Env. Sci. TechnoL, 4,765-8. Young, D. R. 0974). Cadmium and Mercury in the Southern California Bight, TM 216, Southern California Coastal Water Research Project, E1Segundo, CA. Young, D. R., McDermott, D. J., Heesen, T. C. & Jan, T. K. (1975). Pollutant lnputs and Distributions off Southern California. In Marine Chemistry in the Coastal Environment, pp. 424-39. ed. T. M. Church. Washington DC: American Chemical Society.

Heavy Metal Accumulation in Estuarine Sediments in a Historical Mining of Cornwall Sediments in the Hayle estuary in a historical mining areaof Cornwall have been found to contain exceptionally high concentrations of tin, arsenic, copper, lead, tungsten and zinc. In this study, the distribution of these heavy metals is correlated with pollution from past mining activity through mine waste discharge into streams, and changes which took place at the time of the development of the Upton Towans.

The H a y l e estuary is bottle-neck shaped and has an area o f a p p r o x i m a t e l y 2 k m ~ (Fig. 1). Near the m o u t h of the estuary on theinland side, the Hayle H a r b o u r splits up the estuary into a north-eastern o f f s h o o t and a south-western offshoot. The construction o f the H a y l e H a r b o u r which has included a canal in the north-eastern o f f s h o o t has led to an acceleration in silting rate o f the estuary away f r o m the h a r b o u r channels. On the seaward side, the estuary connects up with St. Ives Bay, splitting the U p t o n Towans, a stretch of blown sand deposit f o r m e d during two storms in 1750 and 1869 (Salmon, 1973) into two bodies. The hinterland o f the H a y l e estuary consists essentially of shales and sandstones o f Devonian age intruded by granite. Associated with the granite are n u m e r o u s mineral lodes in which occur minerals rich in tin, arsenic, copper, lead, tungsten and zinc. A m o n g these metals, tin and copper have been mined in the past. In the St. Hilary area, where wastes f r o m ore dressing operations were discharged into the River Hayle, the mines date back at least to the eighteenth century (Dines, 1956). Losses in the treatment o f Cornish tin ores during the early twentieth century must have exceeded 33070 (Thomas, 1913), and in some cases it a p p r o a c h e d 60070. Since all the mines utilize stream water in ore concentration, waste material

discharged into streams can find their way down into the estuary. In this study, the main objective was to determine the vertical distribution of tin and its associated heavy metals in the estuarine sediment, and to evaluate their significance in reflecting past mining pollution. The disposition of the Hayle estuary makes it an effective sediment trap for the land detritus. Most of the resistate ore-minerals and also those originally mobilized ore elements which have been transported by the river as a b s o r b e d c o m p o n e n t s o f colloids are trapped (Hosking & Ong, 1963--4).

Methods Vertical sections o f estuarine sediments were sampled using a 15 cm diameter bucket auger during low tide at three selected locations (Fig. 1). Because o f the design of the bucket auger, some sample mixing was unavoidable and special care was taken during the lowering and removal of the auger f r o m the drill-hole to avoid scrapping material f r o m another horizon. At each auger station, sediment was split according to variations in grain size a n d / o r colour, and the splits were transferred into polythene bags in situ. In the laboratory, entire sample splits were sieved with an 8-mesh sieve (BSS) to remove gravel. After drying at 60°C, samples were split with a Jones riffle down to a b o u t 100 g before grinding and homogenization using an agate T e m a mill. Tin and lead were determined by optical emission spectroscopy (Nichol & H e n d e r s o n - H a m i l t o n , 1965). Copper, iron, manganese, zinc and calcium were determined by atomic absorption spectroscopy following digestion with a 4:1 nitric-perchloric acid mixture. The 147