滨海滩涂不同围垦年代垦区农作物重金属累积特征及其与氮、磷的关系

为探明滨海滩涂围垦区农作物重金属累积特征及其与围垦年代、作物氮磷含量及化学计量比的关系,采集盐城地区不同围垦年代(围垦20、30、40、60年)农田4种主要作物(大麦、小麦、油菜、蚕豆)样品63个,测定了其根、茎叶和籽粒中Cd、Cu、Zn、Pb、Hg、As及全氮(N)、全磷(P)和粗蛋白(CP)含量,分析了重金属累积特征及与围垦年代、N、P、CP及N/P比的关系,并采用单因子污染指数法和内梅罗综合污染指数法对重金属污染程度和安全水平进行了评价。结果表明,1)围垦农田作物整株各指标含量分别为Cd (0.52±0.94)、Cu (12.98±16.00)、Zn (34.93±27.91)、Pb (3.50±5.88)、Hg (0.0063±0.0063)、As (1.94±3.72) mg·kg~(-1)及N(13.69±8.27)、P (5.98±2.24)、CP (79.55±49.54) g·kg~(-1);籽粒中则分别为(0.0059±0.020)、(1.83±1.48)、(11.13±4.45)、(0.09±0.30)、(0.0023±0.0036)、(0.0021±0.0048) mg·kg~(-1)及(19.21±7.68)、(6.04±1.64)、(111.78±47.81) g·kg~(-1); 2)作物重金属均表现为根茎叶籽粒,N和CP与之相反,表现为根茎叶籽粒,而P则表现为根籽粒茎叶; 3)不同围垦年代之间作物重金属、N、P、CP含量、N/P比及综合污染指数(Pz)均没有显著差异(P0.05); 4)各作物籽粒6种重金属单因子污染指数均值均小于1,除个别样品Pb超标(超标率11%)外,其他重金属均未超标; 5)作物籽粒重金属Pz均值为0.38,表明该地区作物重金属总体处于安全级,但大麦、小麦、油菜籽粒均有样品Pb含量超过警戒线,个别样品甚至达到重度污染水平; 6)作物整株各重金属之间、重金属与P之间均存在显著正相关(P0.01),而重金属与N、CP、N/P存在显著负相关(P0.01),在籽粒中则相关性均不显著(P0.05)。以上结果显示,盐城滨海滩涂围垦区作物重金属累积与围垦时间关系不大,其含量目前尚处于可接受范围内,但Pb污染值得关注,作物重金属与P之间存在一定的相互促进作用,而与N存在一定的拮抗作用,高氮低磷的机体养分状况有助于降低重金属含量。

Heavy Metal Accumulation in Crops and its Relationships with Nitrogen and Phosphorus in Different-age Reclaimed Farmlands in Tidal Flat Area

To characterize heavy metal accumulation in crops in reclaimed farmlands of tidal flat and the relationships with reclamation ages (20, 30, 40, 60 years), nitrogen (N), phosphorus (P) and N/P, four crops including barley, wheat, rape, and broad bean were collected in the reclaimed farmlands in Yancheng City. Concentrations of Cd, Cu, Zn, Pb, Hg, As, N, P and crude protein (CP) and N/P stoichiometry in root, leaf, stem and grain were measured and then the relationships among heavy metals, reclamation ages, N, P, CP and N/P ratio were analyzed. Single factor pollution index and Nemerow comprehensive pollution index (Pz) were used to evaluate heavy metal pollution and safety in crops. The results showed that, 1) the concentrations of Cd, Cu, Zn, Pb, Hg, As, N, P, CP in whole plants were (0.52±0.94), (12.98±16.00), (34.93±27.91), (3.50±5.88), (0.0063±0.0063), (1.94±3.72) mg·kg-1 and (13.69±8.27), (5.98±2.24), (79.55±49.54) g·kg-1, respectively. Whereas, the concentrations of these indexes in grains were (0.0059±0.020), (1.83±1.48), (11.13±4.45), (0.09±0.30), (0.0023±0.0036), (0.0021±0.0048) mg·kg-1 and (19.21±7.68), (6.04±1.64), (111.78±47.81) g·kg-1, respectively. 2) The distributions of heavy metals, N and CP, and P in crops followed the order as root>stem and leaf>grain, rootgrain>stem and leaf, respectively. 3) The reclamation ages did not alter the concentrations of heavy metals, N, P, and CP, and N/P ratios, and Pz significantly (P>0.05). 4) The average values of single factor pollution index of heavy metals in grains, except for Pb in a few samples, were less than 1. 5) The average value of Pz was 0.38, which indicates the concentrations of heavy metals in crops in reclamation farmlands were generally safe. While, Pb concentrations in specific samples of barley, wheat and board bean exceeded the warning line. 6) In whole plants, significant positive correlations were observed among heavy metals, as well as between heavy metals and P (P<0.01), and significant negative correlations between heavy metals and N, CP and N/P ratio (P<0.01). In grains, the correlations were all not significant. Our results showed that reclamation ages rarely affected the heavy metal accumulation in crops in the reclaimed farmlands. The Pb pollution is urgently needed to be concerned and the risk of all other heavy metals are acceptable. In crops P likely promotes the accumulation of heavy metals, while nitrogen disables them, so high N with low P may reduce risk of heavy metals in crops.