BACKGROUNDHeavy metal elements in sediment can migrate in an active state under natural action, which has potential bioavailability and potential regional ecological risks. The use of near-infrared spectroscopy (NIRS) technology to study the response mechanism of samples of different matrices can provide a non-destructive and rapid analysis method for evaluating the active state of heavy metals and provide a basis for ecological risk research.

OBJECTIVESTo reveal the characteristics of active metal elements in lagoonal wetland sediment and evaluate their ecological risk.

METHODSSediment core and soil samples near by the drilling site were analyzed using both spectral and chemical method. NIR spectra of dry-freezed sample were collected by infrared spectrometer with integrating sphere. Based on the near infrared spectroscopy analysis technique, near infrared spectrum were collected by the integrating device within range of 4000-10000cm^-1 (1000-2500nm), at the resolution of 2cm^-1. Meanwhile the chemical mobile fractions of heavy metal elements were extracted from soil and sediment samples by diluted nitric acid, the dissolved concentrations of Co, Ni, Cu, Zn, Cd, Pb were determined by inductively coupled plasma-mass spectrometry (ICP-MS). With both chemical and spectral predicted value, the partial least squares regression prediction model had been developed and applied to determine mobile fraction of Co, Ni, Cu, Zn, Cd and Pb.

RESULTSArea of absorption peaks at 7290-6390cm^-1 and 4683-4000cm^-1 related to O-H strentching along with AlAl-OH and Al(Mg)-OH bending indirectly indicate the active content of heavy metals. Spectral prediction results show that the changes in the active components of Co, Ni, Cu, Zn, Cd and Pb in the sediments of the Qilihai in the past 100 years corresponded to the three obvious changes from 1934 to 1948, 1956 to 1963, and 1976 to the present. The temperature increase also corresponded to large-scale human disturbances such as the construction of the Qilihai Reservoir in 1980.

CONCLUSIONSThe total and mobile fractions of Co, Ni, Cu, Zn, Cd and Pb in Qilihai sediments were lower than the ecological risk threshold specified in the national standard. The ecological risk of heavy metals released from wetlands towards nearby villages and farmland in the Qilihai catchment area was extremely low.