parts per million (ppm)
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在研制出一种检测仪器由足够灵敏度监测到土壤里百万分之几的矿物质之后，他发现新泽西土壤里在丧失宝贵的微量元素。
After developing a measuring instrument sensitive enough to detect minerals in soil in parts-per-million, he discovered New Jersey soils were losing valuable trace elements.
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