工業園區鄰近沿海區域牡蠣重金屬濃度之時序與空間變化機制

台灣西部沿岸地區的養殖牡蠣重金屬汙染問題一直以來都是被關注的問題，但過去研究多偏向利用牡蠣累積金屬的特性作為汙染指標，對這些污染來源與性質以及牡蠣如何累積金屬與金屬富集是否有差異，與差異原因卻鮮少探討。　　本論文研究分析2020年11月到2021年11月新竹香山濕地牡蠣養殖區牡蠣群體體內與其所處棲地表層沉積物中微量金屬變化，包含銅、鋅、鉛、鎘、汞、鐵、鋁。本研究使用持續一年時間的採樣樣本來探討香山地區的牡蠣與沉積物中微量金屬的時間與空間分布以及變化機制，以及採集垂直沉積物樣本量測年份與重金屬汙染關係。　　結果顯示出，牡蠣群體體內各種重金屬濃度呈現區域性及季節性之變化。牡蠣體內重金屬濃度以區域性分布呈北高南低的趨勢，應為香山地區南北河川汙染源差異導致。季節性變化則呈現冬高夏低的濃度變化，造成原因可能與季風帶來之懸浮顆粒攪動以及牡犡體自身生長因素有關。　　本研究指出，牡蠣體內重金屬具有兩種特性之分：1. 生物生長控制；2. 環境控制，主要以顆粒濃度高低決定。銅、鋅等牡蠣生長所需金屬之濃度在牡犡體內呈現良好正相關；而鉛、鐵濃度與鋁矽酸岩類與鋁等親顆粒性金屬鋁成正相關。銅、鋅受牡犡生長影響而呈生物累積性，而鉛、鐵、鋁元素應為海水中懸浮顆粒經過牡蠣濾食後殘留在牡蠣體內，受懸浮顆粒含量多寡所控制。根據岩芯垂直沉積物歷史紀錄分析指出自新竹工業興起的1980年代，本研究區域新竹香山牡蠣養殖區汙染相比20年前已降低許多，故可能顯示河川污染源降低導致。　　本研究指出底棲性生物牡蠣內金屬濃度高低受生物生長與環境因子所控制，環境提供額外金屬，含可利用（如銅、鋅等）與不可利用（如鉛），可利用金屬可在牡蠣體內富集，不可利用金屬則藉由濾食後排放，故呈季節性變化。

關鍵字

牡蠣重金屬；沉積物重金屬；生物累積；金屬在牡蠣體內機制

並列摘要

Heavy metal contamination of oysters in coastal areas of western Taiwan has been a long time concern, but past studies have mostly used the accumulation of metals by oysters as an indicator of pollution. The sources and nature of these contaminants, and whether there are differences in how oysters accumulate metals and metal enrichment, and the reasons for these differences have rarely been discussed. 　　This study analyzed the heavy metals in oysters and the surface sediments of their habitats, located in Hsinchu Siangshan Wetland, collected between November 2020 and November 2021 bimonthly. Metals analyzed include copper, zinc, lead, cadmium, mercury, iron, and aluminum. This study examined temporal and spatial distribution of metals in oysters and sediments in the Siangshan area using samples collected over a one-year period. And this study also collected and analyzed a sediments core, using Pb-210 method for sedimentation rate as well as analyzed for metal vertical variations. 　　The results showed regional and seasonal variation in heavy metal concentrations. The regional distribution of heavy metal concentrations in the oyster showed relatively a higher concentrations in the north and lower in the south, which should be differences in sources between rivers in the north and south in the area. The seasonal variation in concentrations was higher in winter and lower in summer, probably due to the stirring of suspended particles brought by strong winds during monsoon and variations during seasonal growth. 　　This study show that there are two major mechanisms in altering concentrations of heavy metals in oysters: 1) biological growth control and 2) environmental control, which is mainly determined by the concentration of particles. Concentrations of copper and zinc, which are required for oyster growth, were positively correlated in oyster, this is different from those concentrations of lead and iron, which were positively correlated with aluminum, a major part of aluminosilicates. Copper and zinc are bioaccumulative metals during oyster growth, whereas lead, iron, and aluminum are retained in oysters after filtering by oysters and are controlled by the amount of suspended particulates. Results from metals vertical concentration profiles in sediment show that pollution in Hsinchu Siangshan area decreased in the past 20 years since the 1980s and therefore may indicate a decrease in the pollution sources region. 　　This study indicates that the concentrations of heavy metals in bottom dwelling oysters were controlled by the biological growth and environmental factors. The environment provides additional metals, including copper, zinc and lead. Copper and zinc are bioaccumulate metals, which could be enriched in oysters. Lead are not bio-essential metals, but, could also enriched in oysters when particles are abundant.