The concentrations of heavy metals, Cd, Hg, Pb, Cu and As in marine sediments from 138 sites located in the Beidaihe near-shore area of Bohai bay, were analyzed to find out the distribution characteristics of these heavy metals. Potential Ecological Risk index were adopted to assess the heavy metals contamination, and the assessment results indicated that the content of heavy metals in this area is in a low to moderate level, while high values were found in the southwest and northeast region, and the value in the middle region is comparatively low. The high pollution hazard sites were close to the Renzaohe estuary and Shihe estuary and the high risk is mainly led by Hg.
The study area is located at Beidaihe near-shore area of Bohai Bay, which belongs to Qinhuangdao city, Hebei Province. It is a famous holiday resorts and important Aquatic products culture zones in Bohai Bay. There are rivers running into the Bohai Bay, including Shihe, Tanghe, Daihe, Yanghe, Renzaohe, Dapuhe, etc. which bring various rich nutrients to the shore, together with pollutants emitted from land. The Beidaihe near-shore area, with shallow water depth and smooth currents, is conducive to various types of pollutants accumulation in the sediment. Due to the long time residual characteristic, easily enrichment feature and huge repairable difficulty, Heavy metals are likely to be the most important pollutants in marine sediment, which are also easily to be transferred along the food chain and proved having badly negative impact on aquatic life and human health [
One hundred and thirty eight un-disturbing samples were collected by Julong-180 drilling rig from sediments in Beidaihe near-shore area ranged between 119˚20'E - 119˚50'E and 39˚40'N - 40˚00'N in July, 2011 (
Hakanson [
where
Based on the research results from Hakanson [
Class | |||||
---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | |
(0, 40) | [40, 80) | [80, 160) | [160, 320) | [320, +∞) | |
(0, 75); [75, 150) | [150, 225); [225, 300) | [300, 450); [450, 600) | [600, +∞) | ||
Level | Nile to very low; low | Lower-moderate; higher-moderate | High; very high | Extremely high | Ultra high |
(1) Distribution characteristic in surface sediments
The general level of heavy metal content is low in sediments.
Cu concentration looks more apparent at 31st and 16th sites while the content of As is more heavy at 3rd and 31st sites and value of Pb is more serious at 20th, 15th and 23rd sites (
Concentrations of Cu, Pb, Hg and Cd, with the highest value in near-shore of Renzaohe estuary and urban inshore area of Qinghuangdao, have a trend of higher from near-shore to sea, while As has a trend of lower (
Except that the coefficient of variation of Cu (73%) is more than 50%, other four kinds of heavy metal coefficient of variations are all smaller, indicating that there is no obvious content distribution difference throughout the study area (
(2) Distribution characteristic in profiles sediments
The concentration of Cu varies in range of 6.59 - 59.35 mg/kg, with mean value of 21.81 mg/kg, while As varies in range of 1.33 - 17.13 mg/kg with mean value of 7.30 mg/kg and the content of Pb varies in range of 6.38 - 41.32 mg/kg, with mean value of 20.62 mg/kg. At the same time, the concentration of Hg varies in range of 0.013 - 0.087 mg/kg with mean value of 0.037 when the concentration of Cd whose mean value is 0.089 varies in range of 0.041 - 0.335 mg/kg. Compared with background values, the Hg pollution is most serious while Cu pollution is the second most serious among all these five heavy metals.
In profile I (
In profile II (
In profile III (
Statistic feature | Cu | As | Pb | Hg | Cd |
---|---|---|---|---|---|
Range | 5.03 - 66.26 | 2.42 - 13.52 | 7.85 - 45.17 | 0.016 - 0.06 | 0.047 - 0.186 |
Mean | 18.90 | 6.70 | 19.93 | 0.04 | 0.09 |
Median | 13.69 | 6.50 | 18.88 | 0.04 | 0.07 |
Root-mean-square deviation | 13.76 | 2.15 | 9.35 | 0.01 | 0.04 |
Coefficientof variation | 0.73 | 0.32 | 0.47 | 0.32 | 0.48 |
of 0.021 - 0.083 mg/kg with mean value of 0.039 mg/kg; and the concentration of Cd whose mean value is 0.104 varies in range of 0.053 - 0.335 mg/kg. Samples with highest concentration of Hg and Cu are located at the top and middle of 16th drilling. Concentration of Hg has a trend of lower from up-section of 16th drilling and middle-section of 19th drilling to around as soon as Cu.
(1) Assessment result in surface sediments
In the view of all the sample sites(
The potential ecological risk (ir) of each site in the study area is below 250, which is at the range of low to moderate potential ecological risk level. The sites near to the Renzaohe estuary, Shihe estuary and Qinhuangdao City inshore area are with comparatively high risk. The 3rd site at the south area has the highest potential risk with the index 240.60. Combined with the characteristic of heavy metal distribution in this site, the high risk is led by Hg.
(2) Assessment result in profiles sediments
From the result of the single element (Figures 10-12), the index of Cu varies in range of 2.48 - 22.35, with mean value of 8.24, while As varies in range of 1.82 - 23.43 with mean value of 10.02 mg/kg and index of Pb
ranged from 1.63 to 10.57, with mean value of 5.27. Whereas the other two heavy metals pollutions, Hg and Cd, are in range of 33.10 - 221.51 (mean of 94.74) and 13.67 - 111.67 (mean of 29.72) respectively. Incontrovertibly, Hg pollution is most serious among these five heavy metals.
The indexes of potential ecological risk in profiles, with mean value of 147.99 and highest value of 288.40, indicate the heavy metals risk is in a low to higher-moderate level.
The ir of profile I and profile III indicate that the heavy metals risks, in majority of samples, are in low- moderate levels (
Results show that the contents of these five heavy metals are lower at the inshore area of Beidaihe and increase along the coastal lines. The distribution of As is different from others whose peak value lied at the inshore area, which is probably caused by the dissimilar sources. The average contents of Hg and Cu are comparatively higher than other metals.
Based on the assessment result of Potential Ecological Risk, pollution of heavy metals is in a low to moderate level in this area. Those sites nearing to Renzaohe estuary, Shihe estuary and central urban inshore zone are with higher risk comparatively.
This work was financially supported by the Geological Environment Investigation and Assessment in Laizhou Bay Area (12120113003800) and Comparative Research of Groundwater Management in the Coastal Areas in Southeast Asia (RETA 6498).
Hongwei Liu,Zhen Ma, (2015) Distribution and Pollution Assessment of Heavy Metals in Beidaihe Near-Shore Marine Sediments. Journal of Materials Science and Chemical Engineering,03,1-7. doi: 10.4236/msce.2015.312001