trace el·e·ment
noun/ˈtreɪs elɪmənt/
/ˈtreɪs elɪmənt/
- a chemical substance that is found in very small amounts
痕量元素 - a chemical substance that living things, especially plants, need only in very small amounts to be able to grow well
微量元素（生物，尤指植物，生长所需要的微量的化学物质）