福建龙海市土壤与稻米铅地球化学特征分析

Study on Pb Geochemical Characteristics of Soil and Rice in Longhai City,Fujian Province

中国南方红壤区铅的分布特征、运移规律及生物效应尚不明确。本文以福建龙海市土壤和稻米为研究对象,系统分析了土壤铅的分布特征、形态组成、生物富集能力及影响机理,总结了铅在母岩-土壤-稻米迁移过程的富集分配规律。结果表明,龙海市中部区域表层土壤的铅含量高,其余区域较低,92.5%样点值在10~90 mg/kg,对应p H为4.0~7.5,强酸性和碱性土壤铅含量略低;稻米铅(0.018~0.398 mg/kg)超标率仅4.1%,对土壤铅的富集能力较弱(富集系数0.23%±0.16%),所以研究区土壤铅超标时稻米不一定超标。影响土壤铅的主要因素是成土母岩和土壤类型,不同成土母岩区的土壤铅含量规律为:第四纪海积物>第四纪残坡积物>花岗岩和酸性火山岩>佛昙组基性玄武岩,不同土壤类型的铅含量规律为:潮土>滨海盐土>水稻土>红壤>赤红壤>滨海风沙土。土壤铅有效态(离子交换态、水溶态)仅占铅全量的4.95%,强有机态和残渣态等其余形态合计占94.99%,说明土壤铅主要以稳定态存在,难于被植物吸收,进一步为合理解释"土壤铅超标而稻米不超标"这一现象提供了调查依据。研究还表明,稻米铅与表层土壤铅之间无明显相关性,保持土壤p H值在弱酸性至弱碱性范围可降低土壤铅活性。

BACKGROUND： The distribution,migration and biological effects of lead in the red soil region of Southern China are still not clear.OBJECTIVES： To study the soil and rice in Longhai city,Fujian Province,and systematically analyze the distribution characteristics,morphological composition,bioaccumulation ability and influencing mechanism of soil lead,and summarize the enrichment and distribution of lead in the parent rock-soil-rice migration process.METHODS： The content of Pb in parent material and its speciation in top soil,as well as the content of Pb in rice was analyzed complying with a systemic sampling code for agro-ecology research.RESULTS： The top soil in the central area of Longhai city has high lead content,and the remaining areas are relatively low. The 92. 5% sample values range from 10 to 90 mg/kg,corresponding to a p H of 4. 0 to 7. 5,and the lead content in strongly acidic and alkaline soils is slightly lower. 4. 1% of the rice lead（ 0. 018-0. 398 mg/kg） exceeded the standard,indicating that the rice has a weak soil lead enrichment capacity（ enrichment coefficient 0. 23% ± 0. 16%）. Therefore,rice in the study area may not necessarily exceed the standard when lead exceeds the standard. The main factors influencing soil lead are soil-forming parent rocks and soil types. The rules of soil lead content in different parent-rock areas are Quaternary marine sediments 〉Quaternary residual sediments 〉Granite and acid volcanic rocks 〉Fotan Formation basic basalt. The rules of lead content in different soil types were fluvo-aquic〉 coastal saline soil 〉paddy soil 〉red soil 〉red soil 〉coastal aeolian sandy soil.CONCLUSIONS： The soil lead availability status（ ion-exchange state,water-soluble state） accounted for only4. 95% of the total lead,and the strong organic state and residual state accounted for 94. 99% of the total,indicating that soil lead exists mainly in a stable state and is difficult to be absorbed by plants. This provides investigation basis for reasonable interpretation of the phenomenon that the soil exceeds the standard lead and the rice does not exceed the standard. The study also showed that there is no significant correlation between rice lead and surface soil lead,and maintaining soil p H in the weakly acidic to weakly alkaline range can reduce soil lead activity.