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柏油路上舖黏膜層 大雨來時釀危機

2009年05月04日
摘譯自2009年4月29日ENS美國,新罕布夏州,杜爾罕報導;丁秋仁編譯;蔡麗伶審校

柏油路上舖黏膜層,大雨來時釀危機;圖片來源:聯合國一般道路及停車場路面上若舖上黏膜層,不但美觀又閃亮,然而一旦雨水一來,從路面沖刷至附近排水道的可就不只有水分子而己。

由美國新罕布夏大學雷雨中心所進行的新研究發現,柏油路上所舖設的黏膜層若受雨水沖刷,鄰近的溝渠便容易被測得有「多環芳香族碳氫化合物」(PAHs)的反應。

PAHs是燃燒柴油或原油所產生的廢氣中的物質之一,且美國人類健康服務部已合理證實部分PAHs形同致癌物質。

雖然新罕布夏海濱附近的水質或多或少可以檢測出微量的PAHs,不過作為實驗的學校停車場周邊排水道,當被驗出含有高濃度的PAHs時,新罕布夏大學土木工程系助理教授巴耶斯特羅(Tom Ballestero)不免憂心,這個結果所帶來的會是怎麼樣的影響。

任職於同校的雷雨中心兼任教授瓦特(Alison Watts)指出,雖然在原先的設計上,舖設在柏油上的黏膜層遇到大雨應留於路面,不過許多黏膜層的物質實際上會被雨水沖刷,並隨著雨水流入附近的水道和河川。

大部分的PAHs不會在水中溶解,卻相對容易依附在微粒固體上,並且沉澱在湖泊或河床上。據聯邦毒性物質及疾病登記局的研究顯示,微生物是有辦法分解土壤或水中的PAHs,不過得花上數星期至數個月的時間。

雷雨中心的研究鎖定學校停車場附近雨水流經的濕地,並分別檢測停車場上有舖設黏膜層及未舖設黏膜層區塊上頭水與土壤中PAHs的濃度。

儘管在幾次降雨過後,PAHs的濃度變低,不過在舖有黏膜層上的涇流,起初所觀察到的濃度竟超過5,000 ppb,遠高於在未舖之地測得10 ppb的濃度值。

PAHs與其他的化合物不同,不但不易消失且可以長年殘留在環境當中。即使是從舖設黏膜層的停車場被沖刷下來的微量PAHs,可能就足以使原本已遭其他汙染物破壞的水生態系統雪上加霜。
一旦水道中的PAHs濃度增加,人類若又長期曝露在此物質之下,對身體健康固然會產生威脅。不僅如此,舖有黏膜層的馬路,揚起的塵埃也可能挾帶PAHs,對於在路上嬉戲的孩童健康安全又形成另一項隱憂。

巴耶斯特羅教授表示,黏膜層所產生的PAH量並不會籠罩著人類的生活,因此對人體健康還不致於造成重大威脅。不過,不過長期的曝露下體內逐漸累積此種物質,誰也難說不會引發何種病變。

Pavement Sealcoat Contributes Toxins to Stormwater Runoff
DURHAM, New Hampshire, April 29, 2009 (ENS)

Driveways and parking lots may look blacker and shinier with a layer of sealcoating applied to the pavement, but the rainwater running off the surface into nearby streams will be carrying more than oxygen and hydrogen atoms.

New research conducted at the University of New Hampshire Stormwater Center shows that sealcoating contributes to the amount of polyaromatic hydrocarbons entering waterways from stormwater runoff.

More commonly known as PAHs, polyaromatic hydrocarbons are found in diesel and crude oil. The Department of Health and Human Services has determined that some PAHs may reasonably be expected to be carcinogens.

Although small amounts of PAHs are typically found in the waters around the New Hampshire Seacoast, the sudden spike in the hydrocarbon concentrations in water draining from a university parking lot used for research caused Tom Ballestero, UNH associate professor of civil engineering, to be concerned about unknown impacts.

Although it is intended to remain on the pavement surface, much of the sealcoating eventually washes or scrapes off and ends up in nearby streams and rivers, says Alison Watts, affiliate faculty member at the University of New Hampshire Stormwater Center.

Most PAHs do not dissolve easily in water but stick to solid particles and settle to the bottoms of lakes or rivers. Microorganisms can break down PAHs in soil or water after a period of weeks to months, according to the federal Agency for Toxic Substances.

On-site stormwater drains off the parking lot and into a nearby swale. The PAH concentration was measured in the water and sediments coming from the sealcoated and unsealed parking lot sections.

Sealcoating led to a rapid increase in PAH concentrations in the initial runoff - up to 5,000 parts per billion, much higher than the 10 ppb levels released from the unsealed lot, although concentrations decreased after several rainstorms.

Unlike other compounds, PAHs do not break down easily and persist in the environment for decades. Even a small amount of PAHs coming off sealcoated parking lots may overwhelm an aquatic ecological system already stressed by other contaminants.

Increased PAH concentrations in waterways could be a human health issue if people are exposed to the substance regularly. In addition, dust particles coming from a sealcoated driveway could potentially be troublesome for children who play on the sealed surface.

"You don't see people falling over from PAHs in sealcoat, it's not that big of a health issue," Ballestero says. "But it could be a cumulative exposure problem that gets uglier over time."