Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa

MPB-08422; No of Pages 9 Marine Pollution Bulletin xxx (2017) xxx–xxx

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Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa E. Vetrimurugan a, V.C. Shruti b, M.P. Jonathan b,⁎, Priyadarsi D Roy c, N.W. Kunene d, Lorena Elizabeth Campos Villegas b a

Department of Hydrology, University of Zululand, Private Bag x1001, Kwa Dlangezwa 3886, South Africa Centro Interdisciplinario de Investigaciones y Estudios sobre Medio Ambiente y Desarrollo (CIIEMAD), Instituto Politécnico Nacional (IPN), Calle 30 de Junio de 1520, Barrio la Laguna Ticomán, Del. Gustavo A. Madero, C.P.07340 Ciudad de México, Mexico c Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria C.P. 04510, Coyoacan, Ciudad de México, Mexico d Department of Agriculture, University of Zululand, Private Bag x1001, Kwa Dlangezwa 3886, South Africa b

a r t i c l e

i n f o

Article history: Received 1 January 2017 Received in revised form 9 February 2017 Accepted 14 February 2017 Available online xxxx Keywords: Acid leachable metals (ALMs) Beach sediments Enrichment factor Geoaccumulation index Potential ecological risk South Durban, South Africa

a b s t r a c t South Durban basin of South Africa has witnessed tremendous urban, industrial expansion and mass tourism impacts exerting significant pressure over marine environments. 43 sediment samples from 7 different beaches (Bluff beach; Ansteys beach; Brighton beach; Cutting beach; Isipingo beach; Tiger Rocks beach; Amanzimtoti beach) were analyzed for acid leachable metals (ALMs) Fe, Mg, Mn, Cr, Cu, Mo, Ni, Co, Pb, Cd, Zn and Hg. The metal concentrations found in all the beaches were higher than the background reference values (avg. in μg g−1) for Cr (223–352), Cu (27.67–42.10), Mo (3.11–4.70), Ni (93–118), Co (45.52–52.44), Zn (31.26–57.01) and Hg (1.13–2.36) suggesting the influence of industrial effluents and harbor activities in this region. Calculated geochemical indexes revealed that extreme contamination of Cr and Hg in all the beach sediments and high Cr and Ni levels poses adverse biological effects. © 2017 Elsevier Ltd. All rights reserved.

Coastal zone interfacing between the land and oceans are extremely sensitive to environmental and human induced changes (Clabby, 2010; Wang et al., 2014; Xu et al., 2016a). They are the “sink” for continents as they constantly receive and concentrate pollutants and other negative consequences of developmental activities taking place in the surroundings (Gao and Chen, 2012; Chakraborty, 2017). The coastal zones throughout the world attract a huge number of human populations resulting in disproportionate rapid expansion of economic activities, industries and urban centers consequently posing a major threat to this highly productive zone (Beck et al., 2011; Wilkinson and Salvat, 2012; Barbier, 2016). Trace metal contamination has attained a global attention due to their environmental persistence, non-degradability, biogeochemical recycling and ecotoxicological risks (Forstner and Wittmann, 1979; Sakan et al., 2006; Yang et al., 2012; Xu et al., 2016b). Beach environments supporting variety of economic activities and inhabited by specialized biotic assemblages are exposed to human pressures at various scales and intensities. Beach sediments are excellent reservoirs of trace metals derived through natural weathering processes and anthropogenic inputs like waste disposal, urban effluents discharge and ⁎ Corresponding author. E-mail addresses: [email protected] (E. Vetrimurugan), [email protected] (M.P. Jonathan).

mining activities etc. (El-Sorogy et al., 2016). The accumulation and mobility of trace metals in sediments depends upon various physical and chemical adsorption mechanisms, properties of adsorbed compounds and the nature of sediment matrices (Bastami et al., 2014). The Kwazulu-Natal coast of South Africa has a rich and diverse natural asset providing numerous economic benefits such as marine fishing, port and harbor development, tourism and recreational opportunities (Cooper, 1995; Guastella and Smith, 2014). It is also an enticing tourist destination casting some of the finest beaches in the world and supporting a large sector of the economy. Durban ranks third most populous urban areas in South Africa in the Kwazulu-Natal province with a population of 3.4 million (Statistics South Africa, 2011). Durban is a great tourist destination attracting larger number of tourists in recent years (Fig. 1; South African Tourism: www.zulu.org.za). The South Durban area is considered as the economic hub of Kwazulu-Natal contributing approximately 8% of GDP and 30% of Durban GDP (Chetty, 2005). It is home to two major petrochemical refineries, sugar refinery, several waste water works, numerous toxic waste landfill sites, an airport, the busiest port in Africa, a paper manufacturing plant and a multitude of chemical processing industries (Peek, 2002). The Durban harbor exports products such as manganese, chrome ore, coal, sugar and grain (Roos, 2010). This highly industrialized basin is recognized as pollution “hot spot” (SDCEA, 2016) and is under the limelight of marine pollution,

http://dx.doi.org/10.1016/j.marpolbul.2017.02.036 0025-326X/© 2017 Elsevier Ltd. All rights reserved.

Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

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E. Vetrimurugan et al. / Marine Pollution Bulletin xxx (2017) xxx–xxx

Fig. 1. Graph representing number of tourists visiting Durban, South Africa.

wherein human activities concentrated in the urban zones and industrial activities greatly influence the distribution of toxic metals in marine environments. The present study is aimed to present a baseline data set on the metal concentrations in beach sediments of South Durban and specifically the main objectives were to: 1) determine the concentration pattern of metal concentrations in beach sediments, 2) evaluate the level of metal enrichment using geoaccumulation index (Igeo) and enrichment factor (EF), 3) determine the possible biological effects through potential ecological risk index formulas and, 4) identify the relationship among trace metals and their sources through application of multivariate statistical analysis. The study area extending between 29° 54′ 26.50″ S, 31° 2′ 11.40″ E and 30° 4′ 19.55″ S, 30° 52′ 32.38″ E, the coastal stretch of South Durban from Bluff beach (in the north) to Amanzimtoti beach (in the south) was covered in the present study. The continental shelf offshore of the Durban is extremely narrow and the distribution of shelf sediments is greatly influenced by the powerful Agulhas current (Martin and Flemming, 1988; Cawthra et al., 2012). Geologically the Natal group of rocks comprising arkosic, quartz-arenitic sandstones and conglomerates overlies the basement rocks of Durban (Smith, 1990; Smith et al., 1993; Singh, 2009). The Dwyka group consisting of tillite that was deposited in a glacial environment by retreating ice sheets about 300 million years ago overlies the Natal group (Visser, 1990). With the melting of ice sheet a major transgression occurred resulting in Ecca group formation constituting carbonaceous shales, silt stone and sand stones (Johnson et al., 2006). The Durban coast experiences a warm subtropical climate characterized with summer rainfall and high air humidity. The average minimum and maximum monthly temperatures are 5.8 and 32.6 °C respectively (Mucina and Geldenhuys, 2006), while the average rainfall is ~1000 mm/year (Jury and Melice, 2000). A total number of 43 beach sediment samples were collected from South Durban tourist beaches during August 2014 (Fig. 2). The sampling sites were divided into seven beach regions namely: 1) Bluff beach (S. Nos. 1–8); 2) Ansteys beach (S. Nos. 9–12); 3) Brighton beach (S. Nos. 13–20); 4) Cutting beach (S. Nos. 21–24) [The prime features of these four regions are the presence of Durban harbor, an airport, Mondi Paper mill and two largest oil refineries]; 5) Isipingo beach (S. Nos. 25–28); 6) Tiger Rocks beach (S. Nos. 29–32) [These two regions forms a major industrial area with the presence of South Africa's largest automobile assembly plant and Isipingo River] and 7) Amanzimtoti beach (S. Nos. 33–43) [Popular tourist destination, numerous hotels and resorts in the premises]. The sediment samples were collected from the beach inter-tidal zone using plastic spatula and were placed in polythene plastic bags and later transported to laboratory. The collected samples were oven dried below 40 °C for powdering and further

analysis. The acid leachable metals (ALMs) Fe, Mg, Mn, Cr, Cu, Mo, Ni, Co, Pb, Cd, Zn and Hg in beach sediments were analyzed based on modified EPA 3051A method (2007) and Navarrete-López et al. (2011). Dry powdered sample (1 g) were mixed with 2.5 ml of HNO3, 0.8 ml of HCl and 1 ml of H2O2 and were digested using PFA [Poly(tetrafluoroethylene)] vessel at 119 ± 1.5 °C for 40 min and the final solution was made up to 10 ml after filtration. The ALMs were measured by introducing the final solutions in inductively coupled plasma atomic emission spectroscopy (PerkinElmer ICP-OES Plasma Optima 8300 DV). All reagents used in the present analysis were of analytical grade (J.T. Baker) and Standard Reference Material (SRM No.691029) Loam soil B (Soil sample) was digested and analyzed along with the samples to check the precision of the equipment and the processing of samples, which was within 1.28 to 3.97%. The relationships between ALMs were identified through processing of data in Statistica (Version 8). The spatial distributions of ALMs in beach sediments of South Durban are represented in Fig. 3a–l. The metal concentrations in beach sediments decreased in the following order: Fe N Mg N Cr N Ni N Mn N Co N Cu N Zn N Pb N Mo N Hg N Cd; Ansteys beach: Fe N Mg N Cr N Ni N Mn N Co N Zn N Cu N Pb N Mo N Hg N Cd; Brighton beach: Fe N Mg N Cr N Ni N Mn N Co N Zn N Cu N Pb N Mo N Hg N Cd; Cutting beach: Fe N Mg N Cr N Ni N Mn N Zn N Co N Cu N Pb N Mo N Hg N Cd; Isipingo beach: Fe N Mg N Cr N Ni N Mn N Zn N Co N Cu N Pb N Mo N Hg N Cd; Tiger Rocks beach: Fe N Mg N Cr N Ni N Co N Mn N Cu N Zn N Pb N Mo N Hg N Cd; Amanzimtoti beach: Fe N Mg N Cr N Ni N Mn N Zn N Co N Cu N Pb N Mo N Hg N Cd.

1) Bluff 2) 3) 4) 5) 6) 7)

beach:

The above sequential order of metal concentrations in all the seven beaches shows a similar decreasing trend except for minor variations. The metal concentrations were compared with UCC (Wedepohl, 1995) values to have a better understanding of the enrichment pattern. It was observed that all the beaches were significantly enriched with (all values in μg g−1) Cr (318; 335; 261; 223; 325; 352; 274), Cu (34; 31.6; 32; 27.6; 34; 42; 33.8), Ni (105; 104; 100; 93; 98; 118; 94), Mo (4.4; 4.2; 3.8; 3.1; 3.9; 4.7; 3.7), Co (48.5; 50.7; 47.7; 45.5; 48.4; 52.4; 46.3) and Hg (1.13; 1.17; 1.89; 2.36; 1.33; 1.14; 1.95) compared to UCC. Higher values of Pb (19.3 μg g−1) were observed in Tiger Rocks beach, where as Cutting beach presented higher concentrations of zinc (57 μg g−1). The coastal stretch of South Durban is naturally enriched in Cr, Cu, Ni, Mo and Co due to weathering of the dark coloured carbon-rich

Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

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Fig. 2. Map showing the studied beaches of the South Durban coast, South Africa.

Ecca group shales present in the study area (Singh, 2009; Lehmann, 2014). The average elevated concentrations (in μg g−1) of ALMs like Cr (298), Cu (34) and Ni (102) in beach sediments are mainly derived from the petrochemical wastes discharged from numerous refining industries in the study area (Doyle et al., 2015; Cechinel et al., 2016). The presence of Cr, Cu and Ni can also be linked to shipping, antifouling agents and various harbor based activities (Brady et al., 2014). Among all the studied beach sites, Tiger Rocks beach recorded higher concentrations of Pb (19.3 μg g−1) due to the influence of Oil refinery situated few kilometers away as it is well known that lead is contained in combustion engines and chemically bound with petroleum hydrocarbons (Gubelit et al., 2016). Cutting beach sediments presented an increased concentrations of Zn (57 μg g−1) and Hg (2.36 μg g−1), which clearly

reflects their sources from the Isipingo river and Umlazi canal that have suffered from the chemical pollution of industries, illegal dumping, leaching of poorly planned waste sites and industrial spills (Kalicharran and Diab, 1993; SDCEA, 2016). The distribution of metals in sediments along the South Durban coast is strongly influenced by the Agulhas current, the strongest western boundary current in the world (Lutjeharms, 2006). The Durban Bluff continental shelf is extremely narrow and steep wherein semi-permanent clockwise eddies develop on the inshore region of Agulhas current moving the sediment along north to south direction of Agulhas current (Flemming, 1978; Flemming and Hay, 1988; Ramsay et al., 1996; Cawthra et al., 2012). Comparisons of the average metal concentrations in the present study with those in other beaches and coastal environments are represented in

Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

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Fig. 3. a–l Distribution of metals in seven different tourist beaches of South Durban, South Africa.

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Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

Locations

Extraction type

Metal concentrations

References

Fe

Mg

Mn

Cr

Cu

Mo

Ni

Co

Pb

Cd

Zn

Hg

Worldwide beaches Sandy beaches of Portugal coast Susanoglu beach sediments, Turkey Piscinas beach, Italy Chennai beach, India Huatulco beach, Mexico Acapulco beach, Mexico Lutong Beach, Malaysia Beach soil, Egypt

HCl + HNO3 + HF XRF HCl + HNO3 + HF HCl + HNO3 HCl + HNO3 HCl HCl + HNO3 HCl + HNO3 + HF

12,000–88,000 12,100–16,500 2700–31,500 442 82,296 6549 − −

− − − − − − − −

200–4632 244–464 90–2943 46.84 388.39 90.47 − −

18–133 125–711 − 14.10 149.54 17.86 85.33 51

117–884 4.4–32.1 2.5–51.3 4.05 11.67 6.33 28.81 118

− − − − − − − −

17–89 93–277 0.99–74.5 9.17 11.79 3.41 18.78 113

22–89 16–29.4 0–13.4 5.05 12.75 − − −

35.7–437 3.5–7.7 74–772 19.77 11.11 3.73 12.88 68

− 3.6–5.5 0.2–13.4 0.31 1.46 − − 11.3

38.3–349.3 15.4–20.9 198–3239 9.89 28.63 19.04 17.93 257

− − − − 0.044 − − −

Vidinha et al., 2009 Gurhan, 2009 Caredda et al., 1999 Santhiya et al., 2011 Retama et al., 2016 Jonathan et al., 2011 Nagarajan et al., 2013 Awadallah et al., 1996

Other coastal environments Coastal Bohai Bay, China Bremen Harbor, Germany Coastal sediments, Chile Coast off southwestern Taiwan Saudi coastline, Saudi Arabia Masan Bay, Korea

− HCl + HNO3 + HF HCl + HNO3 XRF − HNO3 + HF + HClO4

− − 17,600–39,800 − − −

− − − − − −

− − − − − −

101.4 − − 73 295 67.1

38.5 87 13.6–28 32 7.39 43.4

− − − − − −

40.7 60 12.2–39.5 35 8.25 28.8

− 6 − − − −

34.7 122 2.90–9.04 44 9.51 44

0.22 − 0.08–1.25 0.56 0.07 1.24

131.1 790 39.1–61.3 158 36.5 206.3

− 0.3 − − − −

Gao and Chen, 2014 Hamer and Karius, 2002 Chandía and Salamanca, 2012. Chen and Selvaraj, 2008. Al-Trabulsy et al., 2013 Hayun et al., 2007

South Africa Richards Bay beaches

HCl + HNO3

5693

−

65.092

9.114

2.696

−

6.412

5.316

8.678

0.742

78.108

0.0032

Vetrimurugan et al., 2016

Present study Bluff Beach Ansteys Beach Brighton Beach Cutting Beach Isipingo Beach Tiger rocks Beach Atoti Beach UCC values

HCl + HNO3 HCl + HNO3 HCl + HNO3 HCl + HNO3 HCl + HNO3 HCl + HNO3 HCl + HNO3 −

4757 4879 4777 4630 4836 4842 4965 31,792

803 1039 975 1036 1012 605 948 13,871

49.05 74.32 63.31 70.60 73.19 51.10 67.49 542

318 335 261 223 325 352 274 35

34.04 31.61 32.22 27.67 34.01 42.10 33.79 14

4.43 4.16 3.80 3.11 3.93 4.70 3.78 1.4

105 105 100 93 98 118 94 19

48.45 50.74 47.76 45.52 48.41 52.44 46.31 12

14.60 15.35 15.15 15.57 16.82 19.30 15.64 17

0.39 0.46 0.40 0.41 0.47 0.27 0.44 0.102

31.46 48.85 44.64 57.01 50.78 31.26 47.98 52

1.13 1.17 1.89 2.36 1.33 1.14 1.95 0.056

Wedepohl, 1995

Sediment quality guidelines TEC PEC

− −

− −

− −

− −

43.4 111

31.6 149

− −

22.7 48.6

− −

35.8 128

0.99 4.98

121 459

− −

MacDonald et al., 2000 MacDonald et al., 2000

Ecotoxicological values LEL SEL ERL ERM

− − − −

20,000 40,000 − −

− − − −

460 1100 − −

26 110 81 370

16 110 34 270

− − − −

16 75 20.9 51.6

− − − −

31 250 46.7 218

− − 1.2 9.6

120 820 150 410

− − − −

USEPA (2001) USEPA (2001) Long et al., 1995 Long et al., 1995

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Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

Table 1 Comparison of studied metal concentrations with other coastal environments worldwide.

All values are expressed in (μg g−1). UCC = Upper Continental Crust (Wedepohl, 1995); TEC: threshold effect concentration; PEC: probable effect concentration; LEL: lowest effect level; SEL: severe effect level; ERL: effects range low; ERM: effects range medium.

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Fig. 4. Results of Igeo values for seven tourist beaches of South Durban, South Africa.

Table 1. The higher concentrations of Cr (avg. 298 μg g−1) in present study are similar to the beach sediments of Turkey, India and Saudi Arabia. Cu (avg. 34 μg g−1) and Pb (avg. 16 μg g−1) concentrations are observed to be lower compared to the beaches of Portugal, Italy, India, Egypt, Germany and Korea. Ni (avg. 102 μg g−1) concentrations in the present study had higher concentrations than reported in all the other beaches worldwide except for Turkey, India and Egypt. Zn (avg. 45 μg g−1) presented lower values than all the beaches except for Brazil, Turkey, Mexico and Malaysia. In comparison with Richards Bay beaches of South Africa, it is clearly evident that (all avg. values in μg g−1) Cr (298), Cu (34), Ni (102), Co (49), Pb (16) and Hg (1.57) presented higher values in beaches of South Durban. In contrast to the Richards Bay region, South Durban basin forms an economic center and is densely populated hosting a major port, numerous petrochemical, paper, textile and automotive industries greatly influencing the metal concentrations in these seven beaches of the present study. The excessive amount of metals in the sediments often affect the marine biota and pose a risk to human health through bioaccumulation and biomagnification in the food chain (Siddique et al., 2009; Suresh et al., 2015). The potential environmental impacts of the metals in the present study were analyzed by comparing with consensus based Sediment Quality Guidelines (SQGs) and ecotoxicological reference values such as Lowest Effect Level (LEL), Severe Effect Level (SEL), Effect Range Low (ERL) and Effect Range Medium (ERM) (Table 1). According to MacDonald et al., 2000, the concentrations below TEC have no adverse effects while the concentrations above PEC indicate more adverse effects over the biota. The values below LEL and ERL suggest no biological effects and the values above SEL and ERM indicate harmful effects on the biological community (USEPA, 2001; Long et al., 1995). Cr (avg. 298 μg g−1) values in the present study exceeds PEC and SEL values suggesting the occurrence of harmful adverse effects more often as well as the Ni (avg. 102 μg g−1) values exceed above PEL, SEL and ERM indicating threat to aquatic life due to their presence in the sediments. Three different geochemical indices: Enrichment factor (EF), geoaccumulation index (Igeo) and potential ecological risk index (RI) were used to assess the degree of contamination and ecological risks in the beach sediments of South Durban. The Upper Continental Crust values (Wedepohl, 1995) were chosen as the reference background values in all the three geochemical indices of the present study. Enrichment factor (EF) is an effective tool in distinguishing metals originating from anthropogenic activities and those from natural crustal contribution (Buat-Ménard and Chesselet, 1979; Armid et al., 2014; Chen et al., 2016). A value in the range of 0.5 ≤ EF ≤ 1.5 suggests that the metals may be entirely from the crustal materials or natural

weathering processes, while EF N 1.5 indicates that a significant portion of metals is from other external sources rather than natural origins (Zhang and Liu, 2002). The enrichment classes used in the present study were defined as follows: EF b 1.5 (no enrichment); EF 1.5 to b 3 (minor enrichment); EF 3 to b5 (moderate enrichment); EF 5 to b10 (moderately severe enrichment); EF 10 to b 25 (severe enrichment); EF 25 to b 30 (very severe enrichment); EF N 50 (extremely severe enrichment) (Sakan et al., 2009). Results in present study indicate extremely severe enrichment (EF N 50) of Cr and Hg in all the beaches of South Durban (Table 3). The metals Cu, Mo, Ni, Co and Cd exhibited moderately severe to severely enrichment in all the beach sediments, whereas Pb and Zn were moderately enriched. Tiger Rocks beach sediments showed higher EF values of Cr (67.5), Cu (20), Mo (22.5), Ni (41.3), Co (29) and Pb (7.6) than compared to the other beaches. The enrichment of these metals in Tiger Rocks beach sediments are related to the industrial effluents draining in this region, which passes through various industries, such as oil refineries, paper, textile, automotive and several other petrochemical industries located in its premises and are enriched in Cr, Cu, Mo, Ni, Co and Pb (Schroder et al., 2000; Thippeswamy et al., 2012; Zhang et al., 2015; Pandey et al., 2016). Cutting beach sediments had the highest enrichment of Hg (EF = 289) and

Fig. 5. Contribution of different metals to potential ecological risk indices in beach sediments of South Durban, South Africa.

Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

E. Vetrimurugan et al. / Marine Pollution Bulletin xxx (2017) xxx–xxx

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Table 2 Calculated enrichment factor (EF) values for seven different beaches in Durban South, South Africa. Beaches

Enrichment factors (EF)

Bluff Beach Ansteys Beach Brighton Beach Cutting Beach Isipingo Beach Tiger rock Beach Atoti Beach

No enrichment (b1.5)

Minor enrichment (b3)

Moderate enrichment (3–5)

Moderately severe enrichment (5–10)

Severe enrichment (10–25)

Very severe enrichment (25–30)

Extremely severe enrichment (N50)

Mg, Mn Mg, Mn Mg, Mn Mg, Mn Mg, Mn Mg, Mn Mg, Mn

– – – – – – –

Zn – – – – Zn –

Pb Pb, Zn Pb, Zn Pb, Zn Pb, Zn Pb Pb, Zn

Cu, Mo Cu, Mo Cu, Mo Cu, Mo Cu, Mo Cu, Mo, Cd Cu, Mo

Ni, Co, Cd Ni, Co, Cd Ni, Co, Cd Cr, Ni, Co, Cd Ni, Co, Cd Ni, Co Ni, Co, Cd

Cr, Hg Cr, Hg Cr, Hg Hg Cr, Hg Cr, Hg Cr, Hg

Zn (EF = 7.6) among all the other beaches suggesting their inputs from effluents brought in through Isipingo river and Umlazi canal draining in this region. The Igeo index which permits assessment of the extent of sediment contamination based on a pollution intensity classification, consisting of seven classes (0–6) was applied in the present study (Muller, 1979; Varol, 2011; Tang et al., 2015). The highest class indicates 100 fold enrichment of metal contamination over the baseline values. As presented in Fig. 4, the Igeo values for Fe, Mg, Mn, Pb and Zn in all the beaches falls in Class 0 indicating practically no contamination. In Class 1, Cu and Mo is observed for all the beaches inferring that they are uncontaminated to moderately contaminated. Ni, Co and Cd fall in Class 2 for all the beaches indicating moderate contamination. The Igeo values for Cr in all the beaches fall in Class 3 suggesting moderately to heavily contamination. The Igeo values for Hg in Bluff, Ansteys, Isipingo and Tiger Rocks beach sediments falls in Class 4 (heavily contaminated) while in Brighton, Cutting and Amanzimtoti in the Class 5 (heavily to extremely contaminated). The beaches of South Durban coast are extremely contaminated with Cr and Hg, which is mainly attributed to the petrochemical wastes from numerous industries situated in their premises and the effluents discharged through Umlazi canal and Isipingo River. The ecological risk index (RI) introduced by Hakanson (1980) to evaluate the potential ecological risk posed by metals in sediments (Cui et al., 2014; Maanan et al., 2015; Zhang et al., 2016) was applied with the aim of achieving a broader assessment of ecological risks caused by the metals in beaches of South Durban. According to Hakanson (1980), the potential ecological risk (RI) of trace metals in sediments can be categorized as follows: Low ecological risk (RI ≤ 150); Moderate ecological risk (150 to ≤ 300); high ecological risk (300 to ≤600) and significantly high ecological risk (N 600). The ecological risk (RI) of the metals in the South Durban beach sediments are ranked in the following order Hg (9245) N Cd (966) N Ni (212) N Cr (134) N Cu (96) N Pb (37) N Zn (7) N Mn (1). The calculated RI values indicate that Hg and Cd contributed the majority of ecological risk in the

South Durban beach sediments. The single ecological risk factor (Eir) contribution to the potential hazard index (RI) for these two metals was 86.42% and 9.03% respectively, while the contribution ratio of Mn, Cr, Cu, Ni, Pb and Zn to the RI was only 4.5% (Fig. 5). The RI values for Mn, Cr, Cu, Pb and Zn were all b150 suggesting a low ecological risk. Ni presented a RI value of 212 indicating a moderate ecological risk whereas the RI values for Cd and Hg were 966 and 9245 suggesting a high ecological risk due to their presence in the beach sediments of South Durban. In order to establish relationships among metals and determine the common source of metals in South Durban beaches, a correlation matrix was performed for metals in the sediments and are represented in Table 2. A strong positive correlation (r2 = 0.56 to 0.87) of Cr, Cu, Mo, Ni, Co, Pb with each other exists indicating a common geochemical processes controlling their spatial variability and due to their analogous property of transport in marine environment. Fe and Mn in the present study did not have any major correlation suggesting a different origin. However, Mn showed significant correlations with Cd (r2 = 0.42), Zn (r2 = 0.87) and Hg (r2 = 0.47) revealing that these elements are significantly scavenged by Mn oxides/hydroxides (Tessier et al., 1979; Gobeil and Cossa, 1993; Oliveri et al., 2016). The lithophilic element Mg forming a major constituent of clay minerals generally presents negative correlations with Cr (r2 = − 0.32), Cu (r2 = − 0.41), Mo (r2 = − 0.54), Ni (r2 = − 0.37), Co (r2 = − 0.12) and Pb (r2 = −0.28) indicating that these metals are not associated with clay minerals. The inter-element relationships of trace metals (Cr, Cu, Mo, Ni, Co, Pb, Cd, Zn and Hg) suggest that they are external as the concentration pattern are high due to anthropogenic activities in the study area such as petrochemical industries, shipping activities, tourism and riverine inputs. Based on our results, the beach sediments in various sections of South Durban coast in South Africa show distributions of trace metals, wherein Cr, Cu, Mo, Ni, Co, Pb, Zn and Hg exceed the reference values. The enrichment of ALMs is attributable to the urbanization, industrial

Table 3 Correlation matrix analysis of tourist beaches in South Durban, South Africa. Fe Fe Mg Mn Cr Cu Mo Ni Co Pb Cd Zn Hg

1.00 – – – – – – – – – – –

Mg 1.00 0.84⁎,†,‡ −0.32⁎ −0.41⁎ −0.54⁎,†,‡ −0.37⁎ – – 0.65⁎,†,‡ 0.84⁎,†,‡ 0.51⁎,†,‡

Mn

1.00 – – – – – – 0.42⁎ 0.87⁎,†,‡ 0.47⁎

Cr

1.00 0.73⁎,†,‡ 0.87⁎,†,‡ 0.69⁎,†,‡ 0.71⁎,†,‡ 0.56⁎,†,‡ – −0.34⁎ –

Cu

1.00 0.78⁎,†,‡ 0.83⁎,†,‡ 0.82⁎,†,‡ 0.64⁎,†,‡ −0.37⁎ −0.37⁎ –

Mo

Ni

Co

Pb

Cd

Zn

Hg

1.00 0.78⁎,†,‡ 0.72⁎,†,‡ 0.43⁎ −0.36⁎ −0.55⁎,†,‡ −0.32⁎

1.00 0.95⁎,†,‡ 0.55⁎,†,‡ −0.44⁎ −0.39⁎ –

1.00 0.58⁎,†,‡ – – –

1.00 −0.36⁎ – –

1.00 0.48⁎ 0.33⁎

1.00 0.52⁎,†,‡

1.00

⁎ p N 0.05. † p N 0.01. ‡ p N 0.001.

Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036

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E. Vetrimurugan et al. / Marine Pollution Bulletin xxx (2017) xxx–xxx

and harbor activities that occur in these areas. The geochemical indices revealed the extreme contamination levels of Cr and Hg in all the beach sediments. The presence of Cr and Ni in the study region poses a threat to the biological community. The marine environment of South Durban coast is experiencing considerable environmental stress due to the anthropogenic activities from industrial and tourism sectors (KMT, 2004; Jaggernath, 2010). Thus, the present study of the metal concentrations in tourist beaches of South Durban coast dictates the need to monitor regularly the levels of pollutants in various components of the marine environment. Acknowledgements Financial assistance awarded to EV from University of Zululand, South Africa through Research and Innovation Scheme (GrantS186/ 14) is greatly appreciated. MPJ wishes to express their thanks to IPN (COFAA, EDI), Mexico. MPJ and PDR thank Sistema Nacional de Investigadores (SNI), CONACyT, México. 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Please cite this article as: Vetrimurugan, E., et al., Metal concentration in the tourist beaches of South Durban: An industrial hub of South Africa, Marine Pollution Bulletin (2017), http://dx.doi.org/10.1016/j.marpolbul.2017.02.036