Feng H, Cochran J K, Hirschberg D J
Marine Sciences Research Center, State University of New York, Stony Brook 11794-5000, USA.
Sci Total Environ. 1999 Sep 30;237-238:401-18. doi: 10.1016/s0048-9697(99)00153-9.
The natural radionuclides 234Th and 7Be have known sources in estuaries and strongly and rapidly associate with particles. They are thus good tracers of the transport and sources of particles in the suspended sediment reservoir, and, by implication, of particle-associated contaminants such as heavy metals. In the Hudson River estuary, 234Th is produced from decay of dissolved 238U, which varies linearly with salinity, while 7Be is added directly to the estuary from the atmosphere. The 234Th/7Be activity ratio eliminates variations in radionuclide specific activities that result from changes in sediment grain size or composition. Sampling in the Hudson under conditions of low and high river flow shows that 234Th/7Be in suspended sediment increases from low salinity to higher salinity waters at all sampling times. The Th/Be activity ratio may thus be used as a tracer of where particles are labeled with these radionuclides in the estuary and of the relative importance of resuspension and particle transport through the estuary. The distribution of heavy metals in the suspended sediment reservoir can be compared with that of 234Th/7Be by normalizing the metals to Fe. Iron and Al are well correlated in suspended sediments of the Hudson, indicating that either element can be used to normalize grain size effects on specific concentrations of metals. Ratios of Ag and Pb to Fe in suspended particles generally increase down-estuary at all sampling times, whereas Cu, Zn and Cd-to-Fe ratios show more scatter and less consistency in trends. Both source(s) and chemical behavior affect the metal/Fe ratios. The strongest positive correlation with 234Th/7Be is seen for Ag/Fe, reflecting the dominance of lower estuary sources of this trace metal to the Hudson. Relationships between Pb/Fe, Cu/Fe and 234Th/7Be are less strong, reflecting multiple sources of these elements. No correlation is seen for Cd/Fe with 234Th/7Be, indicating either a source up-river or release of Cd as its Kd decreases with increasing salinity.
天然放射性核素钍 - 234（(^{234}Th)）和铍 - 7（(^{7}Be)）在河口有已知来源，并且能迅速与颗粒强烈结合。因此，它们是悬浮沉积物库中颗粒输运和来源的良好示踪剂，进而也能用于追踪与颗粒相关的污染物，如重金属。在哈德逊河河口，钍 - 234由溶解态的铀 - 238（(^{238}U)）衰变产生，其含量随盐度呈线性变化，而铍 - 7则直接从大气中进入河口。钍 - 234与铍 - 7的活度比消除了因沉积物粒度或成分变化导致的放射性核素比活度变化。在哈德逊河低流量和高流量条件下进行采样，结果表明在所有采样时间，悬浮沉积物中的钍 - 234与铍 - 7的活度比从低盐度水域向高盐度水域增加。因此，钍与铍的活度比可作为示踪剂，用于确定河口内这些放射性核素标记颗粒的位置，以及再悬浮和颗粒通过河口输运的相对重要性。通过将重金属含量归一化为铁含量，可将悬浮沉积物库中重金属的分布与钍 - 234和铍 - 7的分布进行比较。在哈德逊河的悬浮沉积物中，铁和铝的相关性良好，这表明两种元素均可用于归一化粒度对金属比浓度的影响。在所有采样时间，悬浮颗粒中银和铅与铁的比值通常沿河口向下游增加，而铜、锌和镉与铁的比值则表现出更多的离散性，趋势一致性较差。来源和化学行为都会影响金属与铁的比值。银与铁的比值（(Ag/Fe)）与钍 - 234和铍 - 7的活度比（(^{234}Th/^{7}Be)）呈现出最强的正相关，这反映出该痕量金属在哈德逊河下游来源占主导地位。铅与铁的比值（(Pb/Fe)）、铜与铁的比值（(Cu/Fe)）与钍 - 234和铍 - 7的活度比之间的相关性较弱，这反映出这些元素来源多样。镉与铁的比值（(Cd/Fe)）与钍 - 234和铍 - 7的活度比没有相关性，这表明要么镉的来源在河流上游，要么随着盐度增加，镉的分配系数（(Kd)）降低导致镉释放。
