美國地質調查科學家發現，美國東南部地區有39%的河流藻類產生微囊藻毒素（microcystins）。研究從水質樣本中測出的微囊藻毒素最大值有一公升3.2微克，並未超出世界衛生組織公布一公升10微克的危險值。
美國愛荷華州賓德湖（Lake Binder），藻類花苞製造出能殺死魚類的毒素。圖片來源：eutrophication&hypoxia（CC BY 2.0）
美國地質調查研究化學家洛夫廷（Keith Loftin）指出，「這是第一次針對河流中藻類製造毒素所做的系統性研究。」研究範圍包括阿拉巴馬、喬治亞、北卡羅來納州、南卡羅來納州和維吉尼亞內共75條河流。
「這樣研究意義重大，讓我們對流動的水生態系統中，微囊藻毒素如何產生，有更深的了解。」他說。公共衛生專家和醫學研究者已經研究微囊藻毒素會對人體所造成的症狀，像是嘔吐、皮膚病和較嚴重的肝功能衰竭。這些案例曾經發生在人類、寵物、家畜和野生動物身上。
先前曾對藍藻（cyanobacteria）——製造微囊藻毒素的藍綠澡種類之一——做過相關研究，發現美國東南部74%的地區有藍綠藻會產生毒素。然而，並沒單單針對微囊藻毒素做過研究。
微囊藻毒素是藻毒素（cyanotoxins）中最常被拿來研究、報導的一種。洛夫廷指出，由於微囊藻毒素對人類健康及生態造成的影響愈加明顯頻繁且嚴重，人類對其關注度有上升趨勢。此外，科學家建議進一步研究微囊藻毒素在不同的河流品質、下游水生態系統、湖泊及水霸中對其周遭環境生態健康會造成什麼潛在的影響。
USGS指出，環境健康程度及其他偶然因素會對微囊藻毒素的分布及規模造成什麼影響至今仍鮮少研究。此外，這項研究也提供了全美對藻類毒素的範圍、規模和其來源相關的基本研究資料。
這項研究由USGS水文毒物質計畫及國家水品質評估計畫協助進行，基本研究資料將可促進更進一步的研究，探討其對土地利用及其他可能影響，或創造對藍藻、微囊藻毒素感染途徑。
USGS在聲明中表示，「現正在西北太平洋，以及準備在美國東北和加州進行的研究，將會增進我們了解廣大水生態中藍澡及其產生的毒素。」
Scientists with the U.S. Geological Survey have found toxins produced by algae, known as microcystins, in 39 percent of the small streams assessed in the southeastern United States.
Their study looked at 75 streams in parts of Alabama, Georgia, North Carolina, South Carolina and Virginia.
“This is the first systematic stream survey of algal toxins in the southeastern United States,” said Keith Loftin, the USGS research chemist who led the study.
“It’s important, because it provides a better understanding of the occurrence of these microcystins in aquatic ecosystems with flowing waters,” he said.
Public health practitioners and medical researchers have observed a range of symptoms in humans after exposure to microcystins. Symptoms can include nausea, dermatitis and, in severe cases, liver failure.
Toxicity issues have been reported for humans, companion animals, livestock and wildlife.
Previous research has indicated that cyanobacteria, a form of blue-green algae capable of producing microcystins, were found in 74 percent of the streams assessed throughout the southeastern United States. However, that research did not include the study of the microcystins themselves.
Microcystins are among the most commonly reported and widely studied cyanotoxins, and Loftin says concerns are growing due to apparent increases in the frequency and severity of human and ecological health effects.
The maximum microcystin concentration measured in this study, 3.2 micrograms per liter (µg/L), did not exceed World Health Organization moderate risk thresholds, 10 µg/L, in the streams sampled.
Still, the scientists advise that further research is needed to understand the potential effects of the microcystins on water quality and related environmental health concerns in downstream aquatic ecosystems, lakes and drinking water reservoirs.
The environmental health significance and causal factors controlling the distribution and magnitude of microcystin occurrence remains poorly understood, the USGS says.
Together, these studies will provide baseline data across the United States to understand and document the extent, magnitude, and sources of algal toxins in the environment.
Baseline data from these regional studies are being used to inform new research that will be focused on investigations of land use and other factors that may affect or create new environmental pathways of exposure to cyanobacteria and microcystins.
“Ongoing work by the USGS in the Pacific Northwest and planned work in the northeastern United States and California will expand our understanding of cyanobacteria and toxins in a wider variety of aquatic ecosystems,” the agency said in a statement announcing the findings on microcystins.
Support for this work was provided by the USGS’ Toxic Substances Hydrology Program and the National Water Quality Assessment Program.
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