Metal levels in three intertidal macroalgae in Hong Kong waters

Aquatic Botany, 29 (1988)367-372

367

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Short Communication M E T A L L E V E L S I N T H R E E I N T E R T I D A L M A C R O A L G A E IN HONG KONG WATERS

Y.B. HO

Department of Botany, University of Hong Kong, PokfulamRoad, Hong Kong (HongKong) (Accepted for publication 5 October 1987)

ABSTRACT Ho, Y.B.,1988. MetallevelsinthreeintertidalmacroalgaeinHongKongwaters.AquaL Bot.,29: 367-372. Analyses were made of the levels of Mn, Fe, Ni, Cu, Zn, Cd and Pb in three common intertidal brown algae, namely Endarachne binghamiae J. Ag., Sargassum hemiphyllum (Turn.) C. Ag. and S. vacheUianumGrey., in the southern part of the island of Hong Kong. The results showed that in a descending order of abundance the metals in the algae were Fe > Mn, Zn > Cu, Ni, Pb > Cd. The relatively low to moderate levels of the seven metals in the algae indicate the absence of serious contamination with these metals in the study area.

INTRODUCTION

Increasing attention has been given to the levels of trace metals in the coastal environment. However, metal levels in the waters generally are relatively low which makes their analyses tedious and difficult. Since marine organisms are known to accumulate and concentrate metals to relatively high levels, they are widely used as sentinel organisms to reflect the extent of metal pollution in the coastal waters (e.g. Phillips, 1980). Over 200 species of algae have been recorded in Hong Kong. Despite the relatively rich algal flora, the metal levels in only three intertidal algae (Wong et al., 1979; Ho, 1981 ) have been published. This paper reports on the levels of Mn, Fe, Ni, Cu, Zn, Cd and Pb in three common brown algae in Hong Kong, namely, Endarachne binghamiae J. Ag., Sargassum hemiphyUum (Turn.) C. Ag. and S. vacheUianum Grey. These three algae are used for food and medicine both in China and Japan. Furthermore, the two species of Sargassum have been collected as a source of fertilizer and, more importantly, as raw materials for the algin processing industry in the nearby regions. Thus, all three are seaweeds of economic importance. 0304-3770/88/$03.50

© 1988 Elsevier Science Publishers B.V.

368

MATERIALSAND METHODS Thirteen intertidal sites on Hong Kong Island were selected for study. They are numbered as follows: (1)Big Wave Bay, (2) ShekO Headland, (3) Cape D'aguilar, (4) Turtle Cove, (5) Stanley Main Beach, (6) Chung Hom Kok, (7) South Bay, (8) Middle Bay, (9) Repulse Bay, {10) Deep Water Bay, (11) Wah Fu, (12) Sandy Bay, (13) Lei Yue Mun. Apart from Site 13, all the sites are on the southern side of Hong Kong Island (Fig. 1 ) and are less affected by sewage contamination in comparison with the waters in Victoria Harbour to the north (Ho, 1981 ). About 0.2-1 kg of fresh algae was hand-picked at low tide from the midlittoral (Endarachne) and the lower littoral (S. hemiphyUum and S. vachellianum) positions in February and/or April/May during the growing season. Subject to availability, Endarachne was taken from Sites 1-5 and 7-10, whereas S. hemiphyllum and S. vachellianum were harvested from Sites 1-8, 11-13 and Sites 3-5, 9-11, respectively. A total of 47 samples were collected in this study. In the laboratory, each algal sample was cleared from epiphytes and animals before it was dipped momentarily in distilled water to remove any adherent seawater. It was then dried at 105 °C for 24-48 h and powdered. The sample was re-dried for 3 h before two subsamples of about 1 g each were separately digested in 14M HNO3, the acid evaporated and the metal salts redissolved in 1 M HCI {Ho, 1984). The amounts ofMn, Fe, Ni, Cu, Zn, Cd and Pb in each subsample were determined by flame AAS ( Instrumentation Laboratory 651 ) with background correction and acetylene as fuel. Standards were prepared in 1 M HC1 to within the linear range of the respective metals. Peak heights of the samples were compared with those of the standards. Whenever necessary,

i. 12~

HONGKONG ~,

- ~r~

9

Fig. 1. Map showing the locations of the sampling sites.

Z

369

the samples were diluted with 1 M HC1 to make the metal levels fall within the s t a n d a r d range. Metal levels in the samples were calculated as micrograms metal per gram dry m a t t e r (/~g g - 1 ) . All glassware was precleaned with acid. T h e reagent blanks, prepared by carrying out the whole procedure but in the absence of the sample, indicated t h a t any c o n t a m i n a t i o n of the sample was negligible. Variations in the concentrations of each metal amongst the duplicated subsamples were < 5% in most cases. RESULTS AND DISCUSSION The a m o u n t s of metals in Endarachne, S. hemiphyUum and S. vachellianum in the various sites are given in Tables I, II and III, respectively. The standard deviation readings indicate t h a t few temporal changes in the levels occurred for Ni, Cu, Zn, Cd and Pb. Conversely, considerable but inconsistent temporal variations were found for M n and Fe for the two species of Sargassum. The overall relative abundance of the seven metals in the algae ranged in the order Fe > Mn, Zn > Ni, Cu, Pb > Cd. Endarachne tended to have higher levels of Zn t h a n Mn, while the reverse was found for the two species of Sargassum. T h e levels of M n in the algae were some four to over ten times less t h a n those of Fe, as has generally been observed for other brown algae (Horowitz and Presley, 1977; Agadi et al., 1978; Ishii et al., 1978). Very close correlation ( r = 0.909, P < 0.001 ) was found between the M n and Fe levels in Endarachne. The mean Fe levels in both S. hemiphyllum and S. vacheUianum were similar TABLE I Metal levels (~g g-~ dry weight) (s.d. given in parentheses) in Endarachne bingharniae from nine sites in Hong Kong Island

Big WaveBay (n=2) Shek 0 Headland (n= 1) Cape D'aguilar (n---2) Turtle Cove (n--l) Stanley Main Beach (n = 2) South Bay (n--l) Middle Bay ( n-- 1) Repulse Bay (n--l) Deep Water Bay (n=l) Mean (n=12)

Mn

Fe

Ni

Cu

9.3 (0.7) 9.7 8.1 (1.3) 9.1 8.9 (0.5) 11.4 9.5 12.2 18.2

64 (7) 66 71 (5) 98 94 (2) 140 91 244 289

8.1 (1.3) 6.0 6.8 (0.8) 3.7 4.0 (0.6) 3.6 4.0 4.9 5.8

7.6 (0.6) 4.8 5.2 (1.0) 2.4 4.0 (0.6) 3.8 3.6 6.0 8.8

10.7 (2.9)

129 (78)

5.2 (1.5)

5.1 (1.9)

Zn

Cd

Pb

54 (2) 57 48 (5) 42 58 (4) 24 47 78 39

0.6 (0.0) 0.7 0.8 (0.0) 0.7 0.6 (0.1) 0.5 0.6 0.6 0.6

6.0 (0.8) 11.6 7.5 (0.5) 6.4 5.5 (0.9) 5.4 6.0 7.2 11.3

50 (14)

0.6 (0.1)

7.4 (2.2)

370

TABLE II Metal levels (ttg g-1 dry weight) (s.d. given in parentheses) in Sargassum herniphyUumfrom 11 sites in Hong Kong Island

Big Wave Bay (n--2) Shek O Headland ( n = 2 ) Cape D'aguilar ( n = 3 ) Turtle Cove ( n =-2 ) Stanley Main Beach ( n - 3 ) Chung Hom Kok (n--2) South Bay ( n = 3 ) Middle Bay (n--3) Wah Fu (n--2) Sandy Bay ( n = 1 ) Lei Yue Mun ( n = l ) Mean (n=24)

Mn

Fe

Ni

Cu

Zn

Cd

Pb

19 (0.1) 26 (12) 18 (1.4) 24 (4.2) 21 (12) 37 (10) 73 (50) 101 (40) 15 (0.9) 320 23

150 (6) 194 (128) 241 (82) 198 (100) 112 (20) 1566 (126) 246 (119) 409 (72) 218 (80) 400 516

10.4 (0.2) 12.1 (0.5) 12.6 (1.3) 9.2 (0.2) 8.1 (0.5) 11.6 (0.8) 9.5 (0.7) 10.1 (1.2) 7.3 (0.3) 12.2 8.7

5.4 (0.8) 5.9 (0.7) 6.5 (1.4) 2.8 (0.2) 2.5 (0.1) 4.1 (0.5) 2.8 (0.1) 3.7 (0.5) 4.0 (0.8) 5.8 5.2

15 (0.8) 19 (2.0) 23 (3.5) 15 (4.0) 14 (1.6) 35 (3.8) 19 (4.3) 20 (1.6) 18 (2.5) 35 20

0.5 (0.0) 0.6 (0.0) 0.7 (0.0) 0.6 (0.1) 0.5 (0.0) 0.6 (0.0) 0.5 (0.1) 0.6 (0.0) 0.6 (0.0) 0.5 0.6

4.5 (0.4) 5.2 (1.0) 4.2 (0.5) 4.9 (0.1) 4.1 (0.8) 8.5 (0.7) 6.3 (0.7) 7.0 (0.4) 3.6 (0.4) 13.2 4.2

62 (86)

386 (391)

10.2 (1.7)

4.4 (1.3)

21 (6.9)

0.6 (0.1)

6.0 (2.7)

to the levels reported for S. greviUei J. Ag. (Sivalingam, 1978) and S. vulgare J. Ag. ( Shiber, 1980). Algae taken from sites to the east of Stanley Main Beach (Site 5) tended to have lower amounts of Fe in their tissues. This may be because lower amounts of bioavailable Fe were present in the waters in these sites. All but one sample of Endarachne and all samples of S. vachellianum had Ni levels below 7 ttg g-1, whereas S. hemiphyllum contained between 7 and 13 ttg g - 1 Ni in its tissues. Other workers (e.g. Saenko et al., 1976; Agadi et al., 1978 ) reported < 10/~g g - 1 Ni in several Sargassum weeds. The levels of Cu in the three species of algae were rather similar to that reported for S. greviUei (Sivalingam, 1978) but were considerably lower than the mean Cu levels of 18.3/~g g-1 for S. vulgare J.Ag. (Shiber, 1980) and 42.1 ttg g - 1 for S. dentifolium ( Turn. ) C. Ag. (Wahbeh et al., 1985 ). Since algae in general readily accumulate Cu from seawater, the relatively low Cu levels found in this study indicate that little contamination of the metal, if any, is present in the southern part of Hong Kong Island. Apparently, both Endarachne and S. vacheUianum have greater capacities

371 TABLE III Metal levels (/~g g - ~dry weight) (s.d.given in parentheses) in Sargassum vacheUianumfrom six sites in Hong Kong Island

Cape D'aguilar ( n-- 2 ) Turtle Cove ( n - - l ) Stanley Main Beach (n-- 1) Middle Bay ( n-- 2 ) Repulse Bay ( n = 3 ) WahFu (n--2) Mean ( n = 11)

Mn

Fe

Ni

Cu

Zn

Cd

Pb

126 (54) 84 309 108 (20) 94 (33) 54 (16)

364 (292) 86 205 981 (509) 827 (235) 241 (113)

5.8 (1.8) 4.0 6.2 6.0 (1.4) 6.1 (0.4) 4.1 (0.3)

6.0 (1.0) 3.6 6.6 4.2 (0.6) 5.0 (0.2) 4.4 (0.4)

78 (40) 21 130 52 (14) 59 (18) 40 (18)

1.1 (0.3) 0.9 1.7 1.0 (0.1) 1.0 (0.1) 0.8 (0.0)

8.6 (1.2) 10.4 13.1 10.5 (1.1) 11.4 (0.4) 9.4 (0.4)

129 (83)

451 (334)

5.4 (0.9)

5.0 (1.0)

63 (34)

1.1 (0.3)

10.6 (1.4)

to accumulate Zn than S. hemiphyllum since at the same site the mean Zn level in either of the former two algae was often more than twice that in the latter. Studies on Sargassum in many areas showed that they generally had < 100/~g g - 1 Zn in their tissues (e.g. Horowitz and Presley, 1977; Agadi et al., 1978; Ishii et al., 1978). Thus, it seems that members of the genus Sargassum have less capacity to accumulate Zn than other Fucales, including Ascophyllum and Fucus, which can accumulate Zn to over 1000/tg g - i (e.g. Bryan and Hummerstone, 1973; Ho, 1984). However, further investigations are needed to verify this. The Cd levels found here were comparable to those reported by Horowitz and Presley (1977) and Shiber (1980) but somewhat lower than the levels of > 5/~g g-1 in other Sargassum species (Sivalingam, 1978). Overall results indicate that no appreciable Cd contamination occurs in the coastal waters of the southern part of Hong Kong Island. Sargassum vachellianum had higher levels of Pb than S. hemiphyUum and Endarachne (Tables I-III). The amounts of Pb reported for Sargassum sp. (Horowitz and Presley, 1977) and S. grevillei (Sivalingam, 1978) were close to those found in S. hemiphyllum and Endarachne here. To conclude, both interspecific and intraspecific differences were found in the levels of each of the seven metals studied, although such variations were not very great. The relatively low to moderate levels of metals found in the three algae indicate that contamination with these metals in the southern part of Hong Kong Island is not serious.

372 REFERENCES Agadi, V.V., Bhosle, N.B. and Untawale, A.G., 1978. Metal concentration in some seaweeds of Goa {India). Bot. Mar., 21: 247-250. Bryan, G.W. and Hummerstone, L.G., 1973. Brown seaweed as an indicator of heavy metals in estuaries in south-west England. J. Mar. Biol. Assoc. U.K., 53: 705-720. Ho, Y.B., 1981. Mineral element contents in Ulva lactuca L. with reference to eutrophication in Hong Kong coastal v~aters. Hydrobiologia, 77: 43-47. Ho, Y.B., 1984. Zn and Cu concentrations in AscophyUum nodosum and Fucus vesiculosus (Phaeophyta, Fucales) after transplantation to an estuary contaminated with mine wastes. Conserv. Recycl., 7: 329-337. Horowitz, A. and Presley, B.J., 1977. Trace metal concentrations and partitioning in zooplankton, neuston, and benthos from the South Texas outer continental shelf. Arch. Environ. Contam. Toxicol., 5: 241-255. Ishii, T., Suzuki, H. and Koyanagi, T., 1978. Determination of trace elements in marine organisms - I. Factors for variation of concentration of trace elements. Bull. Japan. Soc. Sci. Fish., 44: 155-162 {in Japanese, with English abstract). Phillips, D.J.H., 1980. Quantitative Aquatic Biological Indicators. Applied Science Publishers, London, 488 pp. Saenko, G.N., Koryakova, M.D., Makienko, V.F. and Dobrosmyslova, I.G., 1976. Concentration of polyvalent metals by seaweeds in Vostok Bay, Sea of Japan. Mar. Biol., 34: 169-176. Shiber, J.G., 1980. Trace metals with seasonal considerations in coastal algae and molluscs from Beirut, Lebanon. Hydrobiologia, 69: 147-162. Sivalingam, P.M., 1978. Biodeposited trace metals and mineral content studies of some tropical marine algae. Bot. Mar., 21: 327-330. Wahbeh, M.I., Mahasneh, D.M. and Mahasneh, I., 1985. Concentrations of zinc, manganese, copper, cadmium, magnesium and iron in ten species of algae and sea water from Aquaba, Jordan. Mar. Environ. Res., 16: 95-102. Wong, M.H., Chan, K.Y., Kwan, S.H. and Mo, C.F., 1979. Metal contents of the two marine algae found on iron ore tailings. Mar. Pollut. Bull., 10: 56-59.