A SURVEY ON SERIOUS HEAVY METAL POLLUTION IN WATER ECOSYSTEMS OF CHINA - Salt Marshes - page 187

oil industry and chemical industry. Huabei is distributed with fuel and power industry, and
the oil industry. Huazhong is distributed with iron and steel industry, and machinery industry.
Huadong is distributed with machinery industry, textile and other light industries, and
chemical industry. Huanan is distributed with electricity, textile and sugar industry. Huaxi is
distributed with the iron and steel industry, and non-ferrous metal industry. Xibei is
distributed with petroleum and chemical, machinery manufacturing and textile industry
(Wang 1997). Then, all samples were divided into 7 industrial districts according to the
sampling sites (Appendices Table S2): Dongbei (130 samples), Huabei (159 samples),
Huadong (1136 samples), Huanan (528 samples), Xibei (31 samples), Huaxi (261 samples)
and Huazhong (122 samples). The 2367 samples also were divided into 4 types according to
the types of water bodies (Table 1): Lake (365 samples), River (837 samples), Sea (1045
samples) and Wetlands (120 samples).

Data Analysis

We evaluated the potential ecological risk of heavy metals with Hakanson's ecological
risk index in this study. Hakanson's ecological risk index has been prevalently used as a
diagnostic tool to assess the potential ecological risk of heavy metals pollution in sediments
of water body in recent. This index is constructed by two parts: the discrepancy between
present sample value ( C i d ) and background value of heavy metals ( C i r ) and the difference of
toxicity response of each heavy metal. The index is calculated as the following equations
(Hakanson 1980).

i
f

i
d

i
r

C  C / C

i
f

i
f

i
f

E  T * C

m

 

RI  E

i
f

i 1

Where is the toxic-response factor for a given substance, such as, of As, Cd, Cr,
Cu, Hg, Pb, and Zn is 10, 30, 2, 5, 40, 5 and 5, respectively; is the contamination factor (a
ratio between present concentration values and pre-industrial records in sediments); the
individual potential risks ( ) is the potential ecological risk of a single heavy metal and RI
is the integrated potential risk index of many metals accounted in the analysis for the water
body.
We used the background values of heavy metal in the province of sampling sites as the
background values (Appendices Table S3; Ministry of environmental protection of P. R.
China, 1990). After calculation, we classified RI into 4 grades (Appendices Table S4): Slight
( RI <150), Medium (150≤ RI ≤ 300), Strong (300< RI ≤600), Stronger (>600) and E i f was
divided into 5 grades (Appendices Table S4): Slight ( E i f <40), Medium (40≤ E i f ≤ 80), Strong
(80< E i f ≤160), Stronger (160< E i f ≤320), Very strong (>320).

T

i
f

T

i
f

i
f

E