An Introduction to Environmental Chemistry

included better storage tank containment, regular monitoring of cave conduit

outlets and ventilation of basements in homes at risk. It is hoped that these will

prevent a disaster such as occurred in nearby Louisville, Kentucky, where an

underground sewer explosion travelled 11 blocks, causing damage estimated at

over 43 million dollars.

5.7.2 Natural arsenic contamination of groundwater

Those who have seen Victorian melodramas will know that arsenic is a common

and effective poison; murderers have used the oxide (As 2 O 3 ) successfully for the

last two millennia. Ingestion of just 20 mg of the oxide is said to be lethal (but

see Box 5.5), caused through damage to the stomach and intestines; lower expo-

sures cause cancers. Given this macabre background it is perhaps obvious that

exposure to arsenic in foodstuffs and drinking water should be low. Although tiny

amounts of arsenic occur in some foods, it is typically a water-soluble form of

organic arsenic that is easily excreted. Moreover, most drinking water contains

much less than 5mgl-^1 of inorganic arsenic, such that typical daily intakes are

about 4mg.

Arsenic contamination of drinking waters by industrial and commercial activ-

ities is not particularly commonplace, although arsenic is still used in pesticides

in some underdeveloped countries. Surprisingly, however, natural arsenic conta-

mination of groundwater is now well known, and today affects areas of Argentina,

Taiwan, Vietnam, Cambodia, China, Hungary, Bangaladesh, India and the USA.

The symptoms of low-level arsenic poisoning are dependent on dose received,

but can take up to 10 years to develop, while cancers may take 20 years. It is

therefore important to identify arsenic contamination of water supplies quickly.

178 Chapter Five

180

150

120

Elevation (m)

Lost River

Cave entrance Solution enlarged

fractures

Sinkholes

Toxic and/or explosive

fumes from trapped

chemicals may rise into

homes and businesses

Lost River

rise

Jennings

Creek

0 510

Distance (km)

Ste Genevieve

Limestone

,

St Louis Limestone

Lso Rt iver Chert

Fig. 5.18Cross-section through the Lost River Cave drainage system underlying the city of

Bowling Green, Kentucky, showing potential trap for floating or gaseous contaminants. After

Crawford (1984). With permission from Swets & Zeitlinger Publishers.