稀土元素對青鱂魚的毒性效應與生態風險評估

Abstract

稀土元素 (rare earth elements, REEs) 是指鑭系元素 (La－Lu)、鈧 (Scandium, Sc) 與釔 (Yttrium, Y) 共17種元素的合稱。REEs被廣泛應用在許多領域，如玻璃製造、電子科技、能源、醫療甚至農業等，近年來世界各地的使用量不斷增加，透過各種排放途徑而污染環境，最終累積在水體並可能對水中生物造成威脅，因而被視為新興污染物，目前關於REEs對水生生態的毒理和風險資料不足。本篇研究以青鱂魚 (Oryzias latipes) 作為模式生物，利用急毒性試驗探討13種REEs的 96小時半致死濃度 (96 h- Lethal concentration 50, 96 h-LC50)，以挑選毒性風險及暴露風險較高的Y (LC50 = 1.40 μM)、La (LC50 = 1.55 μM)、Gd (LC50 = 2.15 μM) 和Dy (LC50 = 2.20 μM)，再以7天的暴露實驗量測4種 REEs對青鱂魚的非致死效應，其中La (47.1 nM) 以及Y (220.3 nM) 干擾幼魚泳動行為，La (47.1 nM) 和Dy (86.6與185.2 nM) 抑制體長和體重，La具有相對較高的生物濃縮係數 (bioconcentration factors, BCFs)，La (99.4 nM)、Gd (50.1、99.4及188.8 nM) 與Dy (185.2 nM) 造成暴露魚隻的氧化壓力 (oxidative stress)。本研究利用物種敏感分布 (species sensitivity distribution, SSD) 與評估係數 (assessment factor, AF) 法計算之4種REEs的預期無影響濃度 (predicted-no effect concentration, PNEC) 顯示，PNECAF遠小於PNECSSD，且文獻指出La的環境量測濃度 (measured environmental concentration, MEC) 高 (MECave = 0.47 μg/L; MECmax = 2.41 μg/L)，因此4個REEs之中La的生態風險較高 (RQAF = 2.20–37.11; RQSSD = 0.06–0.78; RQave = 1.13–18.94)。因此，本研究評估之REEs的生態風險隨著環境濃度增加而逐漸提高，特別是La具有較高之毒性風險與暴露風險。

Rare earth elements (REEs), comprising the lanthanide series (La-Lu) along with scandium (Sc) and yttrium (Y), are a group of 17 elements widely used in various fields such as electronics, energy, medicine, and agriculture. The widespread applications lead to their releases into the environment through different routes, ultimately accumulating in the aquatic ecosystem and posing potential threats to the organisms. Consequently, REEs are considered as emerging contaminants. Currently, there is insufficient toxicological and risk data concerning REEs on aquatic ecosystems. In this study, we aim to screen the toxicity potency and ecological risks of REEs. The 96-hour median lethal concentration 50 (96-h LC50) of 13 REEs on larvae of medaka (Oryzias latipes) were first assessed through acute toxicity tests. Y (LC50 = 1.40 μM), lanthanum (La, LC50 = 1.55 μM), gadolinium (Gd, LC50 = 2.15 μM), and dysprosium (Dy, LC50 = 2.20 μM) were identified as 4 REEs with higher toxicity and exposure risks. Then, the 7-day sublethal exposure with medaka larvae showed impacts on swimming behaviors by La (47.1 nM) and Y (220.3 nM), decreases in body length and weight by La (99.4 nM) and Dy (86.6 and 185.2 nM), and higher bioconcentration factors (BCFs) by La. La (99.4 nM), Gd (50.1、99.4 and 188.8 nM) and Dy (185.2 nM) caused oxidative stress to medaka fish. The predicted no-effect concentrations (PNEC) derived from species sensitivity distribution (SSD) and assessment factor (AF) approaches for the 4 studied REEs showed that the PNECAF were drastically lower than the PNECSSD. Additionally, the measured environmental concentration (MEC) of La from literatures was the highest (MECave = 0.47 μg/L; MECmax = 2.41 μg/L), indicating that the ecological risk of La was the most significant (RQAF = 2.20–37.11; RQSSD = 0.06–0.78; RQave = 1.13–18.94). Therefore, our study highlights the increasing environmental risks of REEs, especially La with higher toxicity risks and exposure risks.