工业区户外儿童游乐场地表灰尘重金属污染的磁学响应

Magnetic Response of Heavy Metal Pollution in Playground Dust of an Industrial Area

以南京一个工业区为例,采集户外儿童游乐场地表灰尘样品,并对其进行环境磁学测量以及重金属总量和酸可提取态测定,以探究磁学参数对工业区该类环境介质重金属污染的指示作用.结果表明,地表灰尘样品中磁性矿物以亚铁磁性矿物为主,主要以假单畴-多畴颗粒存在;样品低频磁化率和饱和等温剩磁的平均值分别为939.31×10^(-8)m^3·kg^(-1)和16 618.74×10^(-5)A·m^2·kg^(-1),与城市非工业区相比磁性矿物含量较高.地表灰尘样品平均受到中度到高度的重金属污染,部分磁学参数与重金属总量和酸可提取态占比均显著相关,且与总量的相关性较强,其中,Mn、Ni、Cr总量以及污染负荷指数与非磁滞磁化率和饱和等温剩磁的相关性较高(0.69≤r≤0.86,P<0.01),并具有一致的空间变化特征,且主成分分析结果表明重金属和磁性矿物均主要来自工业活动.因此,部分磁学参数可作为指示工业区户外儿童游乐场地表灰尘重金属污染状况的有效指标.

The use of mineral magnetic measurements as a potential pollution proxy is explored as an alternative means of monitoring heavy metal pollution in playground dust in industrial areas. Dust samples were collected from playgrounds in an industrial area in Nanjing. The magnetic properties of the samples were analyzed, and the total and acid-extractable concentrations of heavy metals were measured. Mineral magnetic concentration parameters [ mean magnetic susceptibility （ χlf ） 939. 31 × 10 - 8 m3·kg - 1 and saturation isothermal remanent magnetization （SIRM） 16618. 74 × 10 - 5 A·m2·kg - 1 ] indicate that the dust samples contain high concentrations of magnetic minerals when compared to the non-industrial zone of the city. High and stable S-ratio values （ mean 0. 97, standard deviation 0. 01） indicate the prominence of ferromagnetic minerals. Low values of anhysteretic remanent magnetization （ χARM ） / χlf （2. 35） and χARM / SIRM （0. 12 × 10 - 3 m·A - 1 ） indicate predominantly coarse pseudo single domain （PSD） and multi-domain （MD） magnetic grain size assemblages. The playground dust is considered moderately to highly polluted, and the enrichment factor values for Cd, Zn, Cu, and Pb indicate extremely high contamination levels in the playground dust. Mineral magnetic parameters [χlf , SIRM, hard isothermal remanent magnetization （HIRM）, χARM , and χARM / SIRM] reveal significant correlations with total and acid-extractable concentrations of the trace metals, and the correlations with total concentrations are stronger. The most significant correlations were found with mineral magnetic concentrations （ χARM and SIRM） and total concentrations of the elements Mn, Ni, and Cr and the Tomlinson pollution load index （PLI） （0. 69≤r≤0. 86, P 〈 0. 01）. Consistent spatial characteristics between them were also found, showing that the total concentrations of heavy metals and magnetic parameter values are higher in the playgrounds near and downwind of the power plant. Results of a principal component analysis indicate that anthropogenic activities （ mainly from coal consumption by power plants） are the main sources for both heavy metals and magnetic minerals. In summary, significant correlations and consistent spatial characteristics between heavy metal contents and magnetic parameters and the same anthropogenic source for heavy metals and magnetic minerals confirm that magnetic parameters could be considered as efficient indicators for heavy metal contamination in the playground dust in industrial areas.