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Assessment of dissolved heavy metals in the Laoshan Bay, China
Marine Pollution Bulletin 149 (2019) 110608
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Assessment of dissolved heavy metals in the Laoshan Bay, China Xiaoyan Wang
a,b,c
d
d
a,b
, Lu Liu , Linlin Zhao , Huanzhi Xu
e,∗
, Xiumei Zhang
T
a
National Engineering Research Center of Marine Facilities Aquaculture, Zhejiang Ocean University, Zhoushan, 316004, PR China Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, 316022, PR China Key Laboratory of Informatization of Habitat Monitoring and Fishery Resource Conservation Research in the East China Sea of Zhejiang Province, Zhejiang Ocean University, Zhoushan, PR China d The First Institute of Oceanography, State Oceanic Administration, Qingdao, 266061, PR China e Fishery College, Zhejiang Ocean University, Zhoushan, 316022, PR China b c
ARTICLE INFO
ABSTRACT
Keywords: Laoshan bay China Dissolved heavy metal Sources
A total of 84 surface seawater samples collected from Laoshan Bay, China during the period of 2017–2018 were analysed for physiochemical parameters and dissolved heavy metal concentrations. Cr and Hg concentrations are significantly higher in May than in November, whereas As, Cd and Pb concentrations are significantly higher in November than in May. The single-contaminator factors showed that the most and least dominant elements were Pb and As in both seasons, respectively. And the contamination degree of Laoshan Bay is low. Cr and Hg concentrations are significantly correlated with the physiochemical parameters except chemical oxygen demand (COD). Cu and Pb concentrations are not correlated with the physiochemical parameters. Principal component analysis is conducted to investigate the traces of the dissolved heavy metals. Ship repair activities during summer fishing moratorium and coal combustion have been identified as the major sources of the traces in the studied area in different seasons.
Semi-enclosed bays are important industrial, aquaculture and populated areas due to their superior natural conditions (Peng, 2015). Served as filters and buffer zones to trap contaminants from continents to the open seas, the environment quality of these bays has become a critical issue accordingly. Heavy metals contamination is one of the most common and serious environmental problems today (Sun et al., 2019). Due to the character of toxicity, non-degradable and bioaccumulation, heavy metal contamination can influence the survival, diversity and richness of species, including marine ecosystems (Achary et al., 2016). And could finally cause adverse effects on human health by seafood consumption (Liu et al., 2019). Heavy metals enter the sea via several major sources, most notably riverine influx, atmospheric deposition, and anthropogenic activities (Kennish, 1996). And the seawater and sediment of the bay serve as a pool of heavy metals released by corresponding areas inputs. Therefore, heavy metals in sediment/seawater are important tracers for anthropogenic activities monitoring (Ranjbar et al., 2017). Heavy metal contamination emanates from a wide range of sources, including point sources (rivers, sewage outflows or dumpling) and non-point sources (atmospheric dry and wet deposition or sediment–water exchange) (Wang et al., 2015). And anthropogenic inputs were suggested to be the main sources of heavy metals in the aquatic environment (Han et al.,
∗
2018). The concentrations and distributions of heavy metals have been extensively investigated worldwide (Dai et al., 2009). However, most of these studies focus on estuary areas and surface sediments (Dai et al., 2009; Liu et al., 2017; Mao et al., 2017). Only few studies have analysed dissolved heavy metals in seawater. The physicochemical parameters are important controlling factors for the accumulation and the availability of heavy metals of the environment (Lin et al., 2013; Ranjbar et al., 2017; Yilmaz and Sadikoglu, 2011). For example, the high salinity of seawater could rapid the heavy metals sedimentation by enhancing the aggregation of suspended particles (Lin et al., 2013). Laoshan Bay is a semi-enclosed bay. It includes the two smaller bays of Aoshan Bay and Xiaodao Bay. As the second largest bay in Qingdao, China, the area of Laoshan Bay is approximately 188 km2. Laoshan Bay is an important spawning ground and habitat of several fishery resources, an important marine culture area for sea cucumber, oyster and a stock enhancement area for shrimp and fish species. Furthermore, Laoshan Bay has been positioned as a new marine economic development demonstration zone in China's development schedule since 2015. The construction and development of this new development zone can potentially increase the discharge of pollutants into the bay, which may influence the traditionally important aquaculture area. However, the information about heavy metal contaminants in Laoshan Bay is rare.
Corresponding author. E-mail address: [email protected] (X. Zhang).
https://doi.org/10.1016/j.marpolbul.2019.110608 Received 4 June 2019; Received in revised form 17 September 2019; Accepted 18 September 2019 Available online 16 October 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin 149 (2019) 110608
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Fig. 1. Map of Laoshan Bay and sampling stations in this study. Table 1 Summary of the physicochemical parameters of two seasons in the seawater in the monitoring area. Season
Concentration
Temperature
DO
pH
Salinity
TIN (mg/L)
SRP (mg/L)
COD (mg/L)
SPM (mg/L)
Spring (May)
Range Mean ± std Range Mean ± std Range Mean ± std
11.8−16.7 13.7 ± 1.4 12.6–20.0 16.4 ± 1.8 11.8−20.0 15.1 ± 2.1
7.28−9.21 8.22 ± 0.48 6.73−8.85 7.42 ± 0.59 6.73−9.21 7.82 ± 0.67
7.28−7.90 7.63 ± 0.16 7.68−8.21 7.91 ± 0.12 7.28−8.21 7.77 ± 0.20
31.4−31.5 31.5 ± 0.03 31.7−32.6 32.2 ± 0.13 31.4−32.6 31.8 ± 0.37
0.005−0.048 0.018 ± 0.010 0.003−0.170 0.074 ± 0.042 0.003−0.170 0.046 ± 0.042
0.002−0.011 0.005 ± 0.002 0.008−0.038 0.021 ± 0.008 0.002−0.038 0.013 ± 0.010
0.33−1.73 0.77 ± 0.27 0.24−2.28 0.82 ± 0.436 0.24−2.28 0.80 ± 0.36
3.67−28.7 13.6 ± 5.45 0.00−20.0 9.78 ± 4.61 0.00−28.7 11.7 ± 5.38
Autumn (November) Annual average values
Thus, it is important to assess the heavy metal contamination in Laoshan Bay. For this purpose, the concentrations of seven dissolved heavy metals as well as physiochemical parameters in surface seawater were measured, to identify their ecological risks and potential sources in Laoshan Bay, China. A total of 42 sampling sites were selected in Laoshan Bay (Fig. 1). Two sampling cruises were conducted in November 2017 and May 2018. The physicochemical parameters, such as water temperature, salinity, suspended particulate matter (SPM), pH, dissolved oxygen (DO), chemical oxygen demand (COD), total inorganic nitrogen (TIN), soluble reactive phosphorus (SRP), of the dissolved heavy metals were determined. All procedures followed the specifications of oceanographic surveys in China (GB 17378.4-2007) (SBQTS, 2008). The dissolved heavy metals (Cr, Cu, Zn, As, Cd, Pb and Hg) in the surface seawater of Laoshan Bay were previously determined, as discussed in our previous paper (Wang et al., 2018). All analytical procedures were
strictly monitored by QA and QC. The standards of the selected heavy metals were purchased from the National Standard Material Centre of China. The blank method, parallel samples and sample spikes were analysed with a set of 10 samples. Spike recoveries ranged from 72.0% to 110.0%. Heavy metals were not observed from the reagents and procedures. The contamination factors (CFs) and contamination degrees (CDs) were calculated for water quality evaluation in the studied area (Hakanson, 1980; Wang et al., 2018). CF and CD can both reflect the pollution level of a heavy metal and the overall trace metals in the media, respectively.
CF =
2
Cheavy metal Cbackground
,
Marine Pollution Bulletin 149 (2019) 110608
X. Wang, et al.
Fig. 2. Spatial distributions of dissolved heavy metals in the surface seawater of Laoshan Bay. Table 2 Dissolved heavy metal concentrations in the surface seawater of Laoshan Bay for two monitoring seasons (μg/L). Season
Concentration
Cr
Cu
Zn
As
Cd
Pb
Hg
Spring
Range Mean ± std Range Mean ± std Range Mean ± std
0.97−2.27 1.67 ± 0.29 0.31−2.71 0.80 ± 0.42 0.31−2.71 1.23 ± 0.57
1.07−2.38 1.53 ± 0.32 0.51−4.50 1.48 ± 0.75 0.51−4.50 1.50 ± 0.57
0.89−3.22 1.40 ± 0.53 0.09−5.71 2.22 ± 1.63 0.09−5.71 1.81 ± 1.27
0.63−1.75 1.07 ± 0.25 0.99−1.59 1.25 ± 0.10 0.63−1.75 1.16 ± 0.212
0.059−0.769 0.133 ± 0.186 0.059−0.470 0.106 ± 0.089 0.059−0.769 0.120 ± 0.145
0.16−9.13 0.85 ± 1.56 0.32−2.74 0.78 ± 0.44 0.16−9.13 0.81 ± 1.14
0.001−0.051 0.027 ± 0.013 ND−0.015 0.003 ± 0.003 ND−0.051 0.015 ± 0.015
Autumn Annual average
contaminant levels of Laoshan Bay were evaluated as recommended by Hakanson (i.e. CF < 1 Low, 1 ≥ CF < 3 Moderate, 3 ≥ CF < 6 Considerable and CF ≥ 6 Very high; CD < 5 Low, 5 ≥ CD < 10 Moderate, 10 ≥ CD < 20 Considerable and CD ≥ 20 Very high) (Hakanson, 1980). Seawater quality depends on both the anthropogenic discharges and the natural physicochemical parameters of the environment (Okoro et al., 2013). The spatial and seasonal differences were analysed on the
n
CD =
CF , i= 1
where Cheavy metal is the concentration of a trace metal, and Cbackground is the background value of the corresponding heavy metal in seawater. Owing to the lack of background data about the studied heavy metals for Laoshan Bay, Grade-one seawater quality standard (GB 3097-1997) of China were used as background concentrations (AQSIQ, 1997). The 3
Marine Pollution Bulletin 149 (2019) 110608 Achary et al. (2016) Alonso Castillo et al. (2013) Peng (2015) Wang et al. (2015) Pan et al. (2014) Lü et al. (2015) Sun et al. (2019) Zhao et al. (2018) Current study (1.93) (0.81)
(1.07) (0.88)
5.48 ND-6.80 0.17–9.55 0.39 0.62–1.46 0.56–2.07 0.20–070. 0.06–8.08 0.16–9.13 1.95 ND-0.480 0.02–0.68 0.19 0.19–0.56 (0.36) 0.14–0.38 (0.28) 0.10-0.30 0.01–1.61 (0.22) 0.059–0.769 (0.120) 0.25–4.02 0.70–1.86 (1.33) 1.13–2.37 (1.40) 0-3.40 0.6–8.5 (2.6) 0.63–1.75 (1.16) 53.96 17.3–90 5.2 13.35–36.55 (23.83) 3.20-6.70 0.7–65.9 (16.8) 0.09–5.71 (1.81) 5.76 ND-2.92 0.16–7.17 3.8 0.87–2.71 (2.02) 12.70–18.40 (15.88) 0.80-4.10 ND-44.5 (3.4) 0.51–4.50 (1.50) 2012–2014 2010 2007–2012 2007 2010 1996–2005 2014-2015 2011-2016 2016–2017 Southwest coast of Bay of Bengal Malaga Bay Bohai Sea, China Jiaozhou Bay, China Dingzi Bay, China Laizhou Bay, China Dalian Bay, China Xiangshan Bay, China Laoshan Bay, China
4.03 ND-1.73 3.04–5.68 (4.10) ND-2.0 (0.22) 0.31–2.71 (1.23)
Pb Cd As Zn Cu Cr Sampling Year Region
Table 3 Concentration ranges of dissolved heavy metals in seawater from different regions of the world (μg/L).
basis of the physicochemical parameters and concentrations of the dissolved heavy metals. Multivariate statistics, such as significance test, Pearson's bivariate correlation and principal component analysis (PCA), were performed with SPSS 21.0. The non-parametric Mann–Whitney U test was used for the significance test (Mendiguchia et al., 2007). The physiochemical characteristics of the surface seawater samples are listed in Table 1. Water temperature, DO, pH, salinity, TIN, SRP, COD and SPM are in the range of 11.8–20.0, 6.73–9.21, 7.28–8.21, 31.4–32.6, 0.003–0.170, 0.002–0.038, 0.24–2.28, 0.24–2.28 and 0.00–28.7, respectively. Seasonal significant differences are obtained for all physiochemical parameters except COD. Temperature, pH, salinity, TIN and SRP are significantly higher in November than in May, whereas DO and SPM are significantly higher in May than in November. The autotrophic production is higher in May than November, so the lower levels of TIN and SRP occurred in May than November (Kennish, 1996). Surface seawater is diluted by low salinity water during summer-half-year (May to September), thus higher salinity occurs in November (Li et al., 2016). And influenced by Asia monsoon, the China coastal current is strong during winter-half-year (October to April), and higher SPM was transported from the Yellow River Estuary into our studied area in November (Li et al., 2016). The spatial and seasonal distributions of the dissolved heavy metals in Laoshan Bay are presented in Fig. 2, whilst the corresponding concentrations in the 42 sampling locations in May and in November are listed in Table 2. The concentrations of trace metals ranged from 0.31–2.71 (average 1.23) for Cr, 0.51–4.50 (average 1.50) for Cu, 0.09–5.71 (average 1.81) for Zn, 0.63–1.75 (average 1.16) for As, 0.059–0.769 (average 0.120) for Cd, 0.16–9.13 (average 0.81) for Pb and ND–0.051 μg/L (average 0.015) for Hg, respectively (Table 2). The mean dissolved heavy metals in the surface seawater are in the order of Zn > Cu > Cr > As > Pb > Cd > Hg. The average dissolved heavy metal concentrations in the surface seawater are 1.23 μg/L for Cr, 1.50 μg/L for Cu, 1.81 μg/L for Zn, 1.16 μg/L for As, 0.12 μg/L for Cd, 0.81 μg/L for Pb and 0.015 μg/L for Hg. Zn and Cu exhibited a relatively higher concentrations, which is in line with most of the researches on dissolved heavy metals. Seasonal significant differences are obtained for Cr, As, Cd, Pb and Hg but not for Cu and Zn. The Cr and Hg concentrations are significantly higher in May than in November, whereas the As, Cd and Pb concentrations are significantly higher in November than in May. The minimum and maximum concentrations of Cr are found in B5 and G5 in November. The minimum and maximum concentrations of Cu are found in I1 and D5 in November. The minimum and maximum concentrations of Zn are found in I4 and A1 in November. The minimum and maximum concentrations of As are found in A3 and G4 in May. The minimum and maximum concentrations of Cd are found in I5 and A1 in May. The minimum and maximum concentrations of Pb are found in F4 in May and D4 in November. The minimum and maximum concentrations of Hg are found in J1 in November and I4 in May. Differences in distribution patterns are apparent, as shown in Fig. 2. The Hg concentrations are higher in Xiaodao Bay than in Aoshan Bay but lower in Xiaodao Bay than in Aoshan Bay in May, which indicate possible seasonal changes of these contaminant sources. Similar spatial distribution patterns are also found for Cr and Zn. Table 3 showed that the concentrations of dissolved heavy metals in the surface seawater of Laoshan Bay were either lower than or comparable with those of the other bays. The Cr concentrations in Laoshan Bay are lower than those in the southwest coast of Bengal Bay and Dingzi Bay (Achary et al., 2016; Pan et al., 2014), but higher than that in Xiangshan Bay (Zhao et al., 2018). The Cu concentrations in Laoshan Bay are comparable with the other bays except Laizhou Bay and Xiangshan Bay (Lü et al., 2015; Zhao et al., 2018). The Zn concentrations in Laoshan Bay are lower than those in the other bays. The As, Cd and Hg concentrations in Laoshan Bay are lower or comparable with or lower than those in the other bays. The Pb concentrations in Laoshan Bay are comparable with those in the other bays but higher than that in
0.003–0.36 0.03–0.08 (0.05) 0.014–0.094 (0.056) 0-0.02 ND-1.402 (0.062) ND–0.051 (0.015)
Hg
References
X. Wang, et al.
4
Marine Pollution Bulletin 149 (2019) 110608
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Table 4 Rates of dissolved heavy metals in the sampling locations that exceed China's sweater quality standards.
Spring Autumn Grade-one seawater quality standard (AQSIQ, 1997) (ug/L) Grade-two seawater quality standard (AQSIQ, 1997) (ug/L) CF CD
Cr
Cu
Zn
As
Cd
Pb
Hg
0% (0%) 0% (0%) 5.00 10.00 0.062–0.542 0.762–10.21
0% (0%) 0% (0%) 5.00 10.00 0.102–0.9
0% (0%) 0% (0%) 20.00 50.00 0.004–0.286
0% (0%) 0% (0%) 20.00 30.00 0.031–0.088
0% (0%) 0% (0%) 1.00 5.00 0.059–0.769
19.05% (0%) 19.05% (4.76%) 1.00 5.00 0.161–9.126
2.38% (0%) 0% (0%) 0.05 0.20 0–1.02
Note: Percentages outside or inside parentheses indicate dissolved heavy metals that exceed the primary standard or the secondary standard of seawater quality in China, respectively.
Fig. 3. CFs and CDs of dissolved heavy metals in Laoshan Bay.
Jiaozhou Bay (Wang et al., 2015). The concentrations of the dissolved heavy metals in Laoshan Bay are assessed in accordance with the seawater quality standards of China, as shown in Table 4. The Cr, Cu, Zn, As and Cd concentrations in Laoshan Bay are lower than the primary seawater quality standard of China. However, 19.05% of the Pb levels exceed this standard. In particular, the Pb concentration is within the range the Grade 2 seawater quality in
May, but 4.76% of the locations exceed the Grade 2 seawater quality in November. Meanwhile, the Hg levels do not exceed the primary seawater quality in November, but 2.38% of the locations exceed this primary seawater quality in May. The concentrations of the dissolved heavy metals in May and November are used for CF and CD calculation, as shown in Table 4 and Fig. 3. The mean single-contaminator factors of the elements in the 42 5
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Table 5 Pearson's bivariate correlation among the physicochemical parameters and heavy metal concentrations in the studied area. Correlation
Temperature
DO
pH
salinity
TIN
SRP
COD
SPM
Cr
Cu
Zn
As
Cd
Pb
Hg
Temperature DO pH Salinity TIN SRP COD SPM Cr Cu Zn As Cd Pb Hg
1 −.777** .561** .546** .258* .523** −.251* −.208 −.657** −.151 −.106 .194 −.114 −.147 −.634**
1 −.408** −.522** −.299** −.490** .332** .247* .578** .132 −.026 −.186 .217* .012 .627**
1 .646** .368** .530** .112 −.174 −.507** −.023 .197 .288** −.233* −.149 −.547**
1 .706** .817** .101 −.346** −.724** −.078 .378** .421** −.079 −.011 −.735**
1 .625** −.022 −.225* −.467** −.130 .292** .335** −.086 .025 −.475**
1 −.013 −.227* −.612** −.070 .233* .317** .020 −.047 −.624**
1 −.017 −.047 .196 .349** .081 .011 .106 −.088
1 .329** −.081 −.024 .004 .313** −.008 .386**
1 .230* −.120 −.101 .208 .103 .657**
1 .242* .276* .174 .137 −.016
1 .337** .113 .144 −.243*
1 .301** .090 −.397**
1 .079 .182
1 −.014
1
Three principal components (PCs) for May are extracted from the PCA through the varimax method. The values can explain for 73.15% of the total dissolved heavy metals in May. In particular, PC1, PC2 and PC3 can explain for 39.95%, 17.85% and 15.35% of the total variance, respectively. Then, three PCs for November are extracted from the PCA through the varimax method. The values can explain for 64.63% of the total dissolved heavy metals in November. In particular, PC1, PC2 and PC3 can explain for 24.62%, 21.16% and 18.85% of the total variance, respectively. The trace heavy metals of As, Cu, Zn, Cr and Cd mainly contribute to PC1, those of Hg contribute to PC2 and those of Pb contribute to PC3 in May. Heavy metals of As, Cu, Zn, Cr, and Cd mainly serves as anthropogenic sources, such as antifouling paints, refining and smelting (Hoffman et al., 2003; Kennish, 1996). Fishing boats were forbidden work with fishing related operations during summer fishing moratorium (about four months from 1st May). Ship repair activities concentrated during summer fishing moratorium. The use of antifouling paints containing heavy metals could increase the risk of contamination through both riverine input and atmospheric deposition into the ocean. So PC1 indicated a possible ship repair activities related resources. Hg mainly serves as an anthropogenic source, and coal combustion is the most important source of atmospheric Hg (Lin et al., 2012; Qiu and Wang, 2016). In addition, the paper pulp industries, pesticides and algaecides in agriculture, mercury electrodes in the chloralkali industry may also contribute to the Hg contamination (Kennish, 1996). So PC2 implies industrial activities. Pb is mostly contributed by oil industries, smelting and leaded gasoline (Ranjbar et al., 2017). So PC3 indicating an atmospheric deposition. The trace heavy metals of Pb, Hg and Zn mainly contribute to PC1, those of Cd, Cr and As contribute to PC2 and those of Cu contribute to PC3 in November. Influenced by monsoon, the atmospheric temperature decreased during winter and lots of coals were used for heating since November in north China. Pb, Hg, and Zn were closely related with fossil fuels combustion (Hoffman et al., 2003; Kennish, 1996). Therefore, PC1 indicated a coal combustion source. Cd, Cr and As are commonly used as fungicides and algaecides, indicating the agriculture related origin of PC2. Cu, as an important element in fertilisers, generally corresponded to the source of PC3. The largest sea cucumber breeding and culture base in China located along of Aoshan bay, the dissolved heavy metals were related with the Mariculture activities in November. The differences in the spatial distributions of the trace metals are apparent, Maintains and overhaul of fishing boats during summer fishing moratorium and coal combustion during winter were the most important heavy metal sources in this study area. Zn contributes mostly to the total trace metal concentration in the current study. The pollution level in Laoshan Bay is low to moderate compared with the other
Table 6 Loadings of dissolved heavy metals for the first three PCs. Parameter
Cr Cu Zn As Cd Pb Hg
Spring (May)
Autumn (November)
PC1
PC2
PC3
PC1
PC2
PC3
.589 .852 .732 .923 .561 .055 −.144
.450 −.106 −.077 −.002 .413 −.033 .926
.195 .243 −.120 .059 .007 .977 −.076
.011 .066 .677 .171 .101 .783 .780
.593 .007 .198 .551 .808 .350 −.104
.493 .868 .340 .278 −.238 .167 −.213
sampling locations are in the order of Pb > Hg > Cr > Cu > Cd > Zn > As in May, whereas the order is Pb > Cu > Cr > Zn > Cd > Hg > As in November. The CFs of Cr, Cu, Zn, As and Cd in Laoshan Bay are low. By contrast, the CF of Pb in Laoshan Bay are from low to high, whereas that of Hg is from low to moderate. These results indicate major contamination pressures from Pb and Hg, which is in line with the results in Xiangshan Bay (Zhao et al., 2018). The CD range of Laoshan Bay is 0.762–10.21, which corresponds to levels from low to considerable contamination. The result further indicates major contamination pressures from Cu and Cr, apart from Pb and Hg, in Laoshan Bay. The distribution and transport of heavy metals are controlled by the physicochemical processes (Kennish, 1996). The correlation coefficients and the physicochemical parameters of the dissolved heavy metal concentrations are shown in Table 5. Positive, negative and uncorrelated relationships are found in the current study. The Cu and Pb concentrations are not related with the physiochemical factors. The Cr and Hg concentrations are positively correlated with DO and SPM but negatively correlated with temperature, pH, salinity, TIN and SRP. The Zn concentrations are positively correlated with salinity, TIN, SRP and COD. The As concentrations are positively correlated with pH, salinity, TIN and SRP. The Cd concentrations are positively correlated with DO and SPM but negatively correlated with pH. Salinity, TIN and SRP have significantly negative correlation with Cr and Hg, but significantly positive correlation with Zn and As. Do and SPM are positively correlated with Cr, Cd and Hg. Temperature parameters are negatively correlated with Cr and Hg. While pH are negatively correlated with Cr, Cd and Hg, but positively correlated with As. The correlations and the possible origins of the dissolved heavy metals in the surface seawater of Laoshan Bay are further evaluated by PCA and heat maps. The Kaiser–Meyer–Olkin (KMO) test is implemented for sampling adequacy. The KMO statistic value is set to 0.666 and 0.651 for May and for November, respectively. Different PCA factors are found between May and November, as shown in Table 6. 6
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bays cited in this paper. Trace heavy metals exist in dissolved phase and particulate phase (Wang et al., 2016), and physicochemical factors can influence the trace metals that exist in these phases. Physicochemical factors, such as temperature, DO, pH, salinity, TIN, SRP, COD and SPM, are significantly correlated with one or more dissolved trace metals in the current study. Hydrography, circulation and dynamics during different seasons should be considered (Li et al., 2016; Naimie et al., 2001).
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Acknowledgments This research was supported by the National Natural Science Foundation of China (41806180, 41776171), and the Open Foundation from Marine Sciences in the First-Class Subjects of Zhejiang Province. References Achary, M.S., Panigrahi, S., Satpathy, K.K., Prabhu, R.K., Panigrahy, R.C., 2016. Health risk assessment and seasonal distribution of dissolved trace metals in surface waters of Kalpakkam, southwest coast of Bay of Bengal. Reg. Stud. Mar. Sci. 6, 96–108. Alonso Castillo, M.L., Sanchez Trujillo, I., Vereda Alonso, E., Garcia de Torres, A., Cano Pavon, J.M., 2013. Bioavailability of heavy metals in water and sediments from a typical mediterranean bay (malaga bay, region of andalucia, southern Spain). Mar. Pollut. Bull. 76, 427–434. AQSIQ, 1997. Sea Water Quality Standard (GB 3097-1997). Administration of Quality Supervision, Inspection and Quarantine. Standard Press of China, Beijing. Dai, M., Peng, S., Xu, J., Liu, C., Jin, X., Zhan, S., 2009. Decennary variations of dissolved heavy metals in seawater of Bohai Bay, North China. Bull. Environ. Contam. Toxicol. 83, 907–912. Hakanson, L., 1980. An ecological risk index for aquatic pollution control.a sedimentological approach. Water Res. 14, 975–1001. Han, H., Pan, D., Zhang, S., Wang, C., Hu, X., Wang, Y., Pan, F., 2018. Simultaneous speciation analysis of trace heavy metals (Cu, Pb, Cd and Zn) in seawater from sishili bay, north Yellow sea, China. Bull. Environ. Contam. Toxicol. 101, 486–493. Hoffman, D.J., Rattner, B.A., Jr-Burton, G.A., Jr-Cairns, J., 2003. Handbook of Ecotoxicology. Kennish, M.J., 1996. Practical Handbook of Estuarine and Marine Pollution. CRC Press marine science series 1-524. Lü, D., Zheng, B., Fang, Y., Shen, G., Liu, H., 2015. Distribution and pollution assessment of trace metals in seawater and sediment in Laizhou Bay. Chin. J. Oceanol. Limnol. 33, 1053–1061. Li, G., Qiao, L., Dong, P., Ma, Y., Xu, J., Liu, S., Liu, Y., Li, J., Li, P., Ding, D., Wang, N., Olusegun A, D., Liu, L., 2016. Hydrodynamic condition and suspended sediment diffusion in the Yellow sea and east China sea. J. Geophys. Res.: Oceans 121, 6204–6222. Lin, Y., Vogt, R., Larssen, T., 2012. Environmental mercury in China: a review. Environ. Toxicol. Chem. 31, 2431–2444. Lin, Y.C., Chang-Chien, G.P., Chiang, P.C., Chen, W.H., Lin, Y.C., 2013. Multivariate
7
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Baseline
Assessment of dissolved heavy metals in the Laoshan Bay, China Xiaoyan Wang
a,b,c
d
d
a,b
, Lu Liu , Linlin Zhao , Huanzhi Xu
e,∗
, Xiumei Zhang
T
a
National Engineering Research Center of Marine Facilities Aquaculture, Zhejiang Ocean University, Zhoushan, 316004, PR China Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, 316022, PR China Key Laboratory of Informatization of Habitat Monitoring and Fishery Resource Conservation Research in the East China Sea of Zhejiang Province, Zhejiang Ocean University, Zhoushan, PR China d The First Institute of Oceanography, State Oceanic Administration, Qingdao, 266061, PR China e Fishery College, Zhejiang Ocean University, Zhoushan, 316022, PR China b c
ARTICLE INFO
ABSTRACT
Keywords: Laoshan bay China Dissolved heavy metal Sources
A total of 84 surface seawater samples collected from Laoshan Bay, China during the period of 2017–2018 were analysed for physiochemical parameters and dissolved heavy metal concentrations. Cr and Hg concentrations are significantly higher in May than in November, whereas As, Cd and Pb concentrations are significantly higher in November than in May. The single-contaminator factors showed that the most and least dominant elements were Pb and As in both seasons, respectively. And the contamination degree of Laoshan Bay is low. Cr and Hg concentrations are significantly correlated with the physiochemical parameters except chemical oxygen demand (COD). Cu and Pb concentrations are not correlated with the physiochemical parameters. Principal component analysis is conducted to investigate the traces of the dissolved heavy metals. Ship repair activities during summer fishing moratorium and coal combustion have been identified as the major sources of the traces in the studied area in different seasons.
Semi-enclosed bays are important industrial, aquaculture and populated areas due to their superior natural conditions (Peng, 2015). Served as filters and buffer zones to trap contaminants from continents to the open seas, the environment quality of these bays has become a critical issue accordingly. Heavy metals contamination is one of the most common and serious environmental problems today (Sun et al., 2019). Due to the character of toxicity, non-degradable and bioaccumulation, heavy metal contamination can influence the survival, diversity and richness of species, including marine ecosystems (Achary et al., 2016). And could finally cause adverse effects on human health by seafood consumption (Liu et al., 2019). Heavy metals enter the sea via several major sources, most notably riverine influx, atmospheric deposition, and anthropogenic activities (Kennish, 1996). And the seawater and sediment of the bay serve as a pool of heavy metals released by corresponding areas inputs. Therefore, heavy metals in sediment/seawater are important tracers for anthropogenic activities monitoring (Ranjbar et al., 2017). Heavy metal contamination emanates from a wide range of sources, including point sources (rivers, sewage outflows or dumpling) and non-point sources (atmospheric dry and wet deposition or sediment–water exchange) (Wang et al., 2015). And anthropogenic inputs were suggested to be the main sources of heavy metals in the aquatic environment (Han et al.,
∗
2018). The concentrations and distributions of heavy metals have been extensively investigated worldwide (Dai et al., 2009). However, most of these studies focus on estuary areas and surface sediments (Dai et al., 2009; Liu et al., 2017; Mao et al., 2017). Only few studies have analysed dissolved heavy metals in seawater. The physicochemical parameters are important controlling factors for the accumulation and the availability of heavy metals of the environment (Lin et al., 2013; Ranjbar et al., 2017; Yilmaz and Sadikoglu, 2011). For example, the high salinity of seawater could rapid the heavy metals sedimentation by enhancing the aggregation of suspended particles (Lin et al., 2013). Laoshan Bay is a semi-enclosed bay. It includes the two smaller bays of Aoshan Bay and Xiaodao Bay. As the second largest bay in Qingdao, China, the area of Laoshan Bay is approximately 188 km2. Laoshan Bay is an important spawning ground and habitat of several fishery resources, an important marine culture area for sea cucumber, oyster and a stock enhancement area for shrimp and fish species. Furthermore, Laoshan Bay has been positioned as a new marine economic development demonstration zone in China's development schedule since 2015. The construction and development of this new development zone can potentially increase the discharge of pollutants into the bay, which may influence the traditionally important aquaculture area. However, the information about heavy metal contaminants in Laoshan Bay is rare.
Corresponding author. E-mail address: [email protected] (X. Zhang).
https://doi.org/10.1016/j.marpolbul.2019.110608 Received 4 June 2019; Received in revised form 17 September 2019; Accepted 18 September 2019 Available online 16 October 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin 149 (2019) 110608
X. Wang, et al.
Fig. 1. Map of Laoshan Bay and sampling stations in this study. Table 1 Summary of the physicochemical parameters of two seasons in the seawater in the monitoring area. Season
Concentration
Temperature
DO
pH
Salinity
TIN (mg/L)
SRP (mg/L)
COD (mg/L)
SPM (mg/L)
Spring (May)
Range Mean ± std Range Mean ± std Range Mean ± std
11.8−16.7 13.7 ± 1.4 12.6–20.0 16.4 ± 1.8 11.8−20.0 15.1 ± 2.1
7.28−9.21 8.22 ± 0.48 6.73−8.85 7.42 ± 0.59 6.73−9.21 7.82 ± 0.67
7.28−7.90 7.63 ± 0.16 7.68−8.21 7.91 ± 0.12 7.28−8.21 7.77 ± 0.20
31.4−31.5 31.5 ± 0.03 31.7−32.6 32.2 ± 0.13 31.4−32.6 31.8 ± 0.37
0.005−0.048 0.018 ± 0.010 0.003−0.170 0.074 ± 0.042 0.003−0.170 0.046 ± 0.042
0.002−0.011 0.005 ± 0.002 0.008−0.038 0.021 ± 0.008 0.002−0.038 0.013 ± 0.010
0.33−1.73 0.77 ± 0.27 0.24−2.28 0.82 ± 0.436 0.24−2.28 0.80 ± 0.36
3.67−28.7 13.6 ± 5.45 0.00−20.0 9.78 ± 4.61 0.00−28.7 11.7 ± 5.38
Autumn (November) Annual average values
Thus, it is important to assess the heavy metal contamination in Laoshan Bay. For this purpose, the concentrations of seven dissolved heavy metals as well as physiochemical parameters in surface seawater were measured, to identify their ecological risks and potential sources in Laoshan Bay, China. A total of 42 sampling sites were selected in Laoshan Bay (Fig. 1). Two sampling cruises were conducted in November 2017 and May 2018. The physicochemical parameters, such as water temperature, salinity, suspended particulate matter (SPM), pH, dissolved oxygen (DO), chemical oxygen demand (COD), total inorganic nitrogen (TIN), soluble reactive phosphorus (SRP), of the dissolved heavy metals were determined. All procedures followed the specifications of oceanographic surveys in China (GB 17378.4-2007) (SBQTS, 2008). The dissolved heavy metals (Cr, Cu, Zn, As, Cd, Pb and Hg) in the surface seawater of Laoshan Bay were previously determined, as discussed in our previous paper (Wang et al., 2018). All analytical procedures were
strictly monitored by QA and QC. The standards of the selected heavy metals were purchased from the National Standard Material Centre of China. The blank method, parallel samples and sample spikes were analysed with a set of 10 samples. Spike recoveries ranged from 72.0% to 110.0%. Heavy metals were not observed from the reagents and procedures. The contamination factors (CFs) and contamination degrees (CDs) were calculated for water quality evaluation in the studied area (Hakanson, 1980; Wang et al., 2018). CF and CD can both reflect the pollution level of a heavy metal and the overall trace metals in the media, respectively.
CF =
2
Cheavy metal Cbackground
,
Marine Pollution Bulletin 149 (2019) 110608
X. Wang, et al.
Fig. 2. Spatial distributions of dissolved heavy metals in the surface seawater of Laoshan Bay. Table 2 Dissolved heavy metal concentrations in the surface seawater of Laoshan Bay for two monitoring seasons (μg/L). Season
Concentration
Cr
Cu
Zn
As
Cd
Pb
Hg
Spring
Range Mean ± std Range Mean ± std Range Mean ± std
0.97−2.27 1.67 ± 0.29 0.31−2.71 0.80 ± 0.42 0.31−2.71 1.23 ± 0.57
1.07−2.38 1.53 ± 0.32 0.51−4.50 1.48 ± 0.75 0.51−4.50 1.50 ± 0.57
0.89−3.22 1.40 ± 0.53 0.09−5.71 2.22 ± 1.63 0.09−5.71 1.81 ± 1.27
0.63−1.75 1.07 ± 0.25 0.99−1.59 1.25 ± 0.10 0.63−1.75 1.16 ± 0.212
0.059−0.769 0.133 ± 0.186 0.059−0.470 0.106 ± 0.089 0.059−0.769 0.120 ± 0.145
0.16−9.13 0.85 ± 1.56 0.32−2.74 0.78 ± 0.44 0.16−9.13 0.81 ± 1.14
0.001−0.051 0.027 ± 0.013 ND−0.015 0.003 ± 0.003 ND−0.051 0.015 ± 0.015
Autumn Annual average
contaminant levels of Laoshan Bay were evaluated as recommended by Hakanson (i.e. CF < 1 Low, 1 ≥ CF < 3 Moderate, 3 ≥ CF < 6 Considerable and CF ≥ 6 Very high; CD < 5 Low, 5 ≥ CD < 10 Moderate, 10 ≥ CD < 20 Considerable and CD ≥ 20 Very high) (Hakanson, 1980). Seawater quality depends on both the anthropogenic discharges and the natural physicochemical parameters of the environment (Okoro et al., 2013). The spatial and seasonal differences were analysed on the
n
CD =
CF , i= 1
where Cheavy metal is the concentration of a trace metal, and Cbackground is the background value of the corresponding heavy metal in seawater. Owing to the lack of background data about the studied heavy metals for Laoshan Bay, Grade-one seawater quality standard (GB 3097-1997) of China were used as background concentrations (AQSIQ, 1997). The 3
Marine Pollution Bulletin 149 (2019) 110608 Achary et al. (2016) Alonso Castillo et al. (2013) Peng (2015) Wang et al. (2015) Pan et al. (2014) Lü et al. (2015) Sun et al. (2019) Zhao et al. (2018) Current study (1.93) (0.81)
(1.07) (0.88)
5.48 ND-6.80 0.17–9.55 0.39 0.62–1.46 0.56–2.07 0.20–070. 0.06–8.08 0.16–9.13 1.95 ND-0.480 0.02–0.68 0.19 0.19–0.56 (0.36) 0.14–0.38 (0.28) 0.10-0.30 0.01–1.61 (0.22) 0.059–0.769 (0.120) 0.25–4.02 0.70–1.86 (1.33) 1.13–2.37 (1.40) 0-3.40 0.6–8.5 (2.6) 0.63–1.75 (1.16) 53.96 17.3–90 5.2 13.35–36.55 (23.83) 3.20-6.70 0.7–65.9 (16.8) 0.09–5.71 (1.81) 5.76 ND-2.92 0.16–7.17 3.8 0.87–2.71 (2.02) 12.70–18.40 (15.88) 0.80-4.10 ND-44.5 (3.4) 0.51–4.50 (1.50) 2012–2014 2010 2007–2012 2007 2010 1996–2005 2014-2015 2011-2016 2016–2017 Southwest coast of Bay of Bengal Malaga Bay Bohai Sea, China Jiaozhou Bay, China Dingzi Bay, China Laizhou Bay, China Dalian Bay, China Xiangshan Bay, China Laoshan Bay, China
4.03 ND-1.73 3.04–5.68 (4.10) ND-2.0 (0.22) 0.31–2.71 (1.23)
Pb Cd As Zn Cu Cr Sampling Year Region
Table 3 Concentration ranges of dissolved heavy metals in seawater from different regions of the world (μg/L).
basis of the physicochemical parameters and concentrations of the dissolved heavy metals. Multivariate statistics, such as significance test, Pearson's bivariate correlation and principal component analysis (PCA), were performed with SPSS 21.0. The non-parametric Mann–Whitney U test was used for the significance test (Mendiguchia et al., 2007). The physiochemical characteristics of the surface seawater samples are listed in Table 1. Water temperature, DO, pH, salinity, TIN, SRP, COD and SPM are in the range of 11.8–20.0, 6.73–9.21, 7.28–8.21, 31.4–32.6, 0.003–0.170, 0.002–0.038, 0.24–2.28, 0.24–2.28 and 0.00–28.7, respectively. Seasonal significant differences are obtained for all physiochemical parameters except COD. Temperature, pH, salinity, TIN and SRP are significantly higher in November than in May, whereas DO and SPM are significantly higher in May than in November. The autotrophic production is higher in May than November, so the lower levels of TIN and SRP occurred in May than November (Kennish, 1996). Surface seawater is diluted by low salinity water during summer-half-year (May to September), thus higher salinity occurs in November (Li et al., 2016). And influenced by Asia monsoon, the China coastal current is strong during winter-half-year (October to April), and higher SPM was transported from the Yellow River Estuary into our studied area in November (Li et al., 2016). The spatial and seasonal distributions of the dissolved heavy metals in Laoshan Bay are presented in Fig. 2, whilst the corresponding concentrations in the 42 sampling locations in May and in November are listed in Table 2. The concentrations of trace metals ranged from 0.31–2.71 (average 1.23) for Cr, 0.51–4.50 (average 1.50) for Cu, 0.09–5.71 (average 1.81) for Zn, 0.63–1.75 (average 1.16) for As, 0.059–0.769 (average 0.120) for Cd, 0.16–9.13 (average 0.81) for Pb and ND–0.051 μg/L (average 0.015) for Hg, respectively (Table 2). The mean dissolved heavy metals in the surface seawater are in the order of Zn > Cu > Cr > As > Pb > Cd > Hg. The average dissolved heavy metal concentrations in the surface seawater are 1.23 μg/L for Cr, 1.50 μg/L for Cu, 1.81 μg/L for Zn, 1.16 μg/L for As, 0.12 μg/L for Cd, 0.81 μg/L for Pb and 0.015 μg/L for Hg. Zn and Cu exhibited a relatively higher concentrations, which is in line with most of the researches on dissolved heavy metals. Seasonal significant differences are obtained for Cr, As, Cd, Pb and Hg but not for Cu and Zn. The Cr and Hg concentrations are significantly higher in May than in November, whereas the As, Cd and Pb concentrations are significantly higher in November than in May. The minimum and maximum concentrations of Cr are found in B5 and G5 in November. The minimum and maximum concentrations of Cu are found in I1 and D5 in November. The minimum and maximum concentrations of Zn are found in I4 and A1 in November. The minimum and maximum concentrations of As are found in A3 and G4 in May. The minimum and maximum concentrations of Cd are found in I5 and A1 in May. The minimum and maximum concentrations of Pb are found in F4 in May and D4 in November. The minimum and maximum concentrations of Hg are found in J1 in November and I4 in May. Differences in distribution patterns are apparent, as shown in Fig. 2. The Hg concentrations are higher in Xiaodao Bay than in Aoshan Bay but lower in Xiaodao Bay than in Aoshan Bay in May, which indicate possible seasonal changes of these contaminant sources. Similar spatial distribution patterns are also found for Cr and Zn. Table 3 showed that the concentrations of dissolved heavy metals in the surface seawater of Laoshan Bay were either lower than or comparable with those of the other bays. The Cr concentrations in Laoshan Bay are lower than those in the southwest coast of Bengal Bay and Dingzi Bay (Achary et al., 2016; Pan et al., 2014), but higher than that in Xiangshan Bay (Zhao et al., 2018). The Cu concentrations in Laoshan Bay are comparable with the other bays except Laizhou Bay and Xiangshan Bay (Lü et al., 2015; Zhao et al., 2018). The Zn concentrations in Laoshan Bay are lower than those in the other bays. The As, Cd and Hg concentrations in Laoshan Bay are lower or comparable with or lower than those in the other bays. The Pb concentrations in Laoshan Bay are comparable with those in the other bays but higher than that in
0.003–0.36 0.03–0.08 (0.05) 0.014–0.094 (0.056) 0-0.02 ND-1.402 (0.062) ND–0.051 (0.015)
Hg
References
X. Wang, et al.
4
Marine Pollution Bulletin 149 (2019) 110608
X. Wang, et al.
Table 4 Rates of dissolved heavy metals in the sampling locations that exceed China's sweater quality standards.
Spring Autumn Grade-one seawater quality standard (AQSIQ, 1997) (ug/L) Grade-two seawater quality standard (AQSIQ, 1997) (ug/L) CF CD
Cr
Cu
Zn
As
Cd
Pb
Hg
0% (0%) 0% (0%) 5.00 10.00 0.062–0.542 0.762–10.21
0% (0%) 0% (0%) 5.00 10.00 0.102–0.9
0% (0%) 0% (0%) 20.00 50.00 0.004–0.286
0% (0%) 0% (0%) 20.00 30.00 0.031–0.088
0% (0%) 0% (0%) 1.00 5.00 0.059–0.769
19.05% (0%) 19.05% (4.76%) 1.00 5.00 0.161–9.126
2.38% (0%) 0% (0%) 0.05 0.20 0–1.02
Note: Percentages outside or inside parentheses indicate dissolved heavy metals that exceed the primary standard or the secondary standard of seawater quality in China, respectively.
Fig. 3. CFs and CDs of dissolved heavy metals in Laoshan Bay.
Jiaozhou Bay (Wang et al., 2015). The concentrations of the dissolved heavy metals in Laoshan Bay are assessed in accordance with the seawater quality standards of China, as shown in Table 4. The Cr, Cu, Zn, As and Cd concentrations in Laoshan Bay are lower than the primary seawater quality standard of China. However, 19.05% of the Pb levels exceed this standard. In particular, the Pb concentration is within the range the Grade 2 seawater quality in
May, but 4.76% of the locations exceed the Grade 2 seawater quality in November. Meanwhile, the Hg levels do not exceed the primary seawater quality in November, but 2.38% of the locations exceed this primary seawater quality in May. The concentrations of the dissolved heavy metals in May and November are used for CF and CD calculation, as shown in Table 4 and Fig. 3. The mean single-contaminator factors of the elements in the 42 5
Marine Pollution Bulletin 149 (2019) 110608
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Table 5 Pearson's bivariate correlation among the physicochemical parameters and heavy metal concentrations in the studied area. Correlation
Temperature
DO
pH
salinity
TIN
SRP
COD
SPM
Cr
Cu
Zn
As
Cd
Pb
Hg
Temperature DO pH Salinity TIN SRP COD SPM Cr Cu Zn As Cd Pb Hg
1 −.777** .561** .546** .258* .523** −.251* −.208 −.657** −.151 −.106 .194 −.114 −.147 −.634**
1 −.408** −.522** −.299** −.490** .332** .247* .578** .132 −.026 −.186 .217* .012 .627**
1 .646** .368** .530** .112 −.174 −.507** −.023 .197 .288** −.233* −.149 −.547**
1 .706** .817** .101 −.346** −.724** −.078 .378** .421** −.079 −.011 −.735**
1 .625** −.022 −.225* −.467** −.130 .292** .335** −.086 .025 −.475**
1 −.013 −.227* −.612** −.070 .233* .317** .020 −.047 −.624**
1 −.017 −.047 .196 .349** .081 .011 .106 −.088
1 .329** −.081 −.024 .004 .313** −.008 .386**
1 .230* −.120 −.101 .208 .103 .657**
1 .242* .276* .174 .137 −.016
1 .337** .113 .144 −.243*
1 .301** .090 −.397**
1 .079 .182
1 −.014
1
Three principal components (PCs) for May are extracted from the PCA through the varimax method. The values can explain for 73.15% of the total dissolved heavy metals in May. In particular, PC1, PC2 and PC3 can explain for 39.95%, 17.85% and 15.35% of the total variance, respectively. Then, three PCs for November are extracted from the PCA through the varimax method. The values can explain for 64.63% of the total dissolved heavy metals in November. In particular, PC1, PC2 and PC3 can explain for 24.62%, 21.16% and 18.85% of the total variance, respectively. The trace heavy metals of As, Cu, Zn, Cr and Cd mainly contribute to PC1, those of Hg contribute to PC2 and those of Pb contribute to PC3 in May. Heavy metals of As, Cu, Zn, Cr, and Cd mainly serves as anthropogenic sources, such as antifouling paints, refining and smelting (Hoffman et al., 2003; Kennish, 1996). Fishing boats were forbidden work with fishing related operations during summer fishing moratorium (about four months from 1st May). Ship repair activities concentrated during summer fishing moratorium. The use of antifouling paints containing heavy metals could increase the risk of contamination through both riverine input and atmospheric deposition into the ocean. So PC1 indicated a possible ship repair activities related resources. Hg mainly serves as an anthropogenic source, and coal combustion is the most important source of atmospheric Hg (Lin et al., 2012; Qiu and Wang, 2016). In addition, the paper pulp industries, pesticides and algaecides in agriculture, mercury electrodes in the chloralkali industry may also contribute to the Hg contamination (Kennish, 1996). So PC2 implies industrial activities. Pb is mostly contributed by oil industries, smelting and leaded gasoline (Ranjbar et al., 2017). So PC3 indicating an atmospheric deposition. The trace heavy metals of Pb, Hg and Zn mainly contribute to PC1, those of Cd, Cr and As contribute to PC2 and those of Cu contribute to PC3 in November. Influenced by monsoon, the atmospheric temperature decreased during winter and lots of coals were used for heating since November in north China. Pb, Hg, and Zn were closely related with fossil fuels combustion (Hoffman et al., 2003; Kennish, 1996). Therefore, PC1 indicated a coal combustion source. Cd, Cr and As are commonly used as fungicides and algaecides, indicating the agriculture related origin of PC2. Cu, as an important element in fertilisers, generally corresponded to the source of PC3. The largest sea cucumber breeding and culture base in China located along of Aoshan bay, the dissolved heavy metals were related with the Mariculture activities in November. The differences in the spatial distributions of the trace metals are apparent, Maintains and overhaul of fishing boats during summer fishing moratorium and coal combustion during winter were the most important heavy metal sources in this study area. Zn contributes mostly to the total trace metal concentration in the current study. The pollution level in Laoshan Bay is low to moderate compared with the other
Table 6 Loadings of dissolved heavy metals for the first three PCs. Parameter
Cr Cu Zn As Cd Pb Hg
Spring (May)
Autumn (November)
PC1
PC2
PC3
PC1
PC2
PC3
.589 .852 .732 .923 .561 .055 −.144
.450 −.106 −.077 −.002 .413 −.033 .926
.195 .243 −.120 .059 .007 .977 −.076
.011 .066 .677 .171 .101 .783 .780
.593 .007 .198 .551 .808 .350 −.104
.493 .868 .340 .278 −.238 .167 −.213
sampling locations are in the order of Pb > Hg > Cr > Cu > Cd > Zn > As in May, whereas the order is Pb > Cu > Cr > Zn > Cd > Hg > As in November. The CFs of Cr, Cu, Zn, As and Cd in Laoshan Bay are low. By contrast, the CF of Pb in Laoshan Bay are from low to high, whereas that of Hg is from low to moderate. These results indicate major contamination pressures from Pb and Hg, which is in line with the results in Xiangshan Bay (Zhao et al., 2018). The CD range of Laoshan Bay is 0.762–10.21, which corresponds to levels from low to considerable contamination. The result further indicates major contamination pressures from Cu and Cr, apart from Pb and Hg, in Laoshan Bay. The distribution and transport of heavy metals are controlled by the physicochemical processes (Kennish, 1996). The correlation coefficients and the physicochemical parameters of the dissolved heavy metal concentrations are shown in Table 5. Positive, negative and uncorrelated relationships are found in the current study. The Cu and Pb concentrations are not related with the physiochemical factors. The Cr and Hg concentrations are positively correlated with DO and SPM but negatively correlated with temperature, pH, salinity, TIN and SRP. The Zn concentrations are positively correlated with salinity, TIN, SRP and COD. The As concentrations are positively correlated with pH, salinity, TIN and SRP. The Cd concentrations are positively correlated with DO and SPM but negatively correlated with pH. Salinity, TIN and SRP have significantly negative correlation with Cr and Hg, but significantly positive correlation with Zn and As. Do and SPM are positively correlated with Cr, Cd and Hg. Temperature parameters are negatively correlated with Cr and Hg. While pH are negatively correlated with Cr, Cd and Hg, but positively correlated with As. The correlations and the possible origins of the dissolved heavy metals in the surface seawater of Laoshan Bay are further evaluated by PCA and heat maps. The Kaiser–Meyer–Olkin (KMO) test is implemented for sampling adequacy. The KMO statistic value is set to 0.666 and 0.651 for May and for November, respectively. Different PCA factors are found between May and November, as shown in Table 6. 6
Marine Pollution Bulletin 149 (2019) 110608
X. Wang, et al.
bays cited in this paper. Trace heavy metals exist in dissolved phase and particulate phase (Wang et al., 2016), and physicochemical factors can influence the trace metals that exist in these phases. Physicochemical factors, such as temperature, DO, pH, salinity, TIN, SRP, COD and SPM, are significantly correlated with one or more dissolved trace metals in the current study. Hydrography, circulation and dynamics during different seasons should be considered (Li et al., 2016; Naimie et al., 2001).
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