Ключевые слова: aged, backdrop, background, bacteria, biohazard, biology, boundary, caution, cement, concept, concrete, conservation, containment, contamination, danger, dangerous, dirty, ebola, eco, ecology, environment, epidemic, fence, flu, grunge, grungy, hazard, hazardous, illustration, infectious, link, nature, nuclear, orange, pollute, pollution, radiation, radioactive, radioactivity, risk, safety, sick, sign, symbol, toxic, wall, warning, waste, weathered, yellow,