In an average winter, highway departments spread some ten million tons of salt to keep roads safe. The corrosive effects are well known, but for years they' re been dismissed with the argument that at around $ 25 a ton, salt is far cheaper than any alternative. Lately, economists have added up the actual costs. The Environmental Protection Agency estimates that salt-induced road damage and vehicle corrosion cost $ 3 billion a year. That does not include damage to underground cables, which adds hundreds of millions to utility bills. Nor does it reflect the cost of brine leaking into porous water pipes, threatening the water supply. Salty water leaches into roadbeds, kills evergreens and poisons streams. The various costs probably add another $ 2 billion to the national salt bill. Scientists estimate the full economic, or 'life cycle,' cost for a ton of salt at $ 500, or 20 times the $ 25 purchase price. That begins to make the switch to calcium magnesium acetate, perhaps the most promising alternative look practical. CMA, made from acetic acid and dolomitic(含白石的) lime, costs $ 600 a ton and has minimal adverse effect. Some researchers believe the cost can be halved by CMA from waste cheese whey or pulp-mill effluent. While CMA and other alternatives are being researched, many cities and states are cutting back on their use of salt. Keeping dispensing equipment in good repair helps reduce the amount spread. Salt spread on road in winter may cause all the following problems except ______.