| 其他摘要 | With the gradually improvement of industrialization and urbanization, and the
soaring increase of energy consumption, the emissions of polycyclic aromatic
hydrocarbons (PAHs) are also increasing. PAHs have long-distance migration potential
and show strong lipophilicity, as well as teratogenic, carcinogenic and mutagenic
properties. They have been widely detected in the atmosphere, water, soil, sediment,
and even organisms and humans. The coastal sea connects the land and the ocean. Huge
amounts of pollutants are discharging into coastal sea by extensively industrial and
human activities from coastal cities and have caused the deterioration of water quality
and have endangering the health of ecosystem and human health. Fifteen priority PAHs
were analyzed in the seawater and sediment from three research cruises on the Bohai
Sea in June, August and November 2019, respectively. The spatial distribution
characteristics and seasonal variations of PAHs in the seawater were investigated for
the first time in the Bohai Sea, and the phase distributions were discussed for PAHs
between two phases (dissolved and particle phase). This paper also studied the
concentration levels, composition profiles and distribution characteristics of PAHs in
the surface sediments, and briefly analyzed the main input pathways of PAHs in the
Bohai Sea. The conclusions of the study are as follows:
PAHs were widely detected in the seawater with a range of 3.16-87.9 ng/L.
Horizontally, high levels were found in nearshore and low in the central of Bohai Sea,
indicating a dominant land-based source of PAHs. Compared with other studies around
the world, the overall PAH levels in the Bohai Sea are at medium levels. The estimated
reserves of PAHs in the seawater are much lower than the total PAHs emissions from
neighboring cities. It is inferred that offshore waters are important environmental media
for the migration and transformation of PAHs in the environment.
In the spring and autumn, there are no obvious difference for vertical distribution
of PAHs in the Bohai Sea, indicating a well-mixed water mass in the Bohai Sea under
the strong influence of the East Asia monsoon. However, relatively high concentrations
of PAHs were found in the surface water than in the bottom water in the central Bohai
Sea in summer. This phenomenon was caused by the formation of vertically
stratifications of water masses in summer and the thermoclines have hindered the
vertical exchange of water bodies. The seasonal variationas showed that total
concentration of PAHs was higher in June than in November. The low concentrations & "
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of PAHs in summer may be due to the fast volatilization of PAHs into the atmosphere
under high-temperature. The decrease in the number of fishing boats during the fishing
ban period may also lower the PAHs concentration from fishing activities. The
increased concentration of PAHs in autumn was related to the discrease of ambient
temperature and the emission from coal-fired heating in northern China. Source
analysis showed that PAHs in the seawater were mainly from the combustion of
biomass and fossil fuels, industrial wastewater and domestic sewage, and ship oil spills
and fuel combustion.
In surface sediment, concentration of PAHs was ranged from 7.23 to 168 ng/g dw,
which showed a slight medium pollution level wordwidely. The estimated reserves of
PAHs in the surface sediments reached to 226 tons, which indicated that the surface
sediments are important sink of PAHs. A positive correlation was found between the
concentrations of PAHs and TOC, indicating TOC content is an important tool for
assessing the pollution level and distribution characteristics of organic pollutants such
as PAHs. Source analysis showed that fossil fuels (such as petroleum and coal) and
biomass combustion are the main sources of PAHs in the surface sediments of the Bohai
Sea.
In summary, as a kind of persistent toxic pollutants discharged from unintentional
production, PAHs were produced inadvertently in daily industrial and domestic
activities. Land-based pollution is the main sources of PAHs. Seawater and sediment
are the two reservoirs of PAHs in the Bohai Sea. PAHs show different scales of
variations vertically and seasonally in the Bohai Sea. PAHs mainly exist in the dissolved
phase in water bodies with mainly low-ring congeners; while PAHs in surface
sediments they were mainly consisted of high-ring congeners. This shows that the more
water-soluble PAHs in water bodies are easily transferred to other sea areas along with
high-temperature volatilization and ocean currents, while the more stable high-ring
PAHs are easily adsorbed or concentrated on particulate matter, and finally settle into
marine sediments. Therefore, the results of this study would help us to better understand
the environmental behavior of PAHs in the marine system, and to provide a reference
for the monitoring and governance of the marine organic pollutants. |
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