2 . Sixty-six years ago, there was one human-built object in Earth’s orbit. It was Sputnik, the world’s first satellite, launched in October 1957. Try to guess how many human-made objects are circling the planet now. Ready?

Your answer is wrong, unless you guessed 100 trillion. That’s a jaw-dropping number. It was provided by an international team of researchers writing in the journal Science. For years, this junk has formed an ever-growing mass near Earth. It’s a danger to spacecraft. The researchers are calling for a global treaty to limit the number of satellites and the amount of rubbish in space.

There are 9,000 active satellites in orbit, the scientists report. That could grow to more than 60,000 by 2030. The rest of that 100 trillion figure includes everything from used-up booster rockets and stray bolts to metal flecks and paint chips. Don’t think a paint chip is harmless. Travelling at 17,500 miles per hour, it can strike a spacecraft hard. The International Space Station is dotted with dents and holes. Astronauts often take shelter in an attached spacecraft to wait out a passing swarm of space debris (残骸). That way, if the station is severely damaged, they can escape in a hurry.

The mess we’ve made in space is like the mess we’ve made in the oceans. Think of the Great Pacific Garbage Patch. It’s a mass of floating junk twice the size of Texas. We’ve had centuries to make the ocean dirty. But it has taken just decades for us to do the same in space. That’s why the Science authors include experts in satellite technology and in ocean plastic pollution. “As a marine biologist, I never imagined writing a paper on space,” writes Heather Koldewey, who works at the Zoological Society of London. Cleaning up space, she says, has a lot in common “with the challenges of tackling environmental issues in the ocean.”

Coauthor Moriba Jah is an aerospace engineering professor at the University of Texas at Austin. “Marine debris and space debris,” he writes, “are both a human-made damage that is unavoidable.”

3 . There are many kinds of pollution, which can be classified by environment, including air pollution, water pollution, and land pollution. Modern society is also concerned about specific types of pollution, such as noise pollution, light pollution and plastic pollution. Pollution of all kinds may not only have negative effects on the environment and wildlife, but also do harm to human health and well-being.

Although environmental pollution can be caused by natural events such as forest fires and active volcanoes, use of the word “pollution” generally means that the wastes have an anthropocentric source—that is, a source created by human activities. Pollution has accompanied humankind ever since groups of people first congregated and remained for a long time in any one place. Indeed, ancient human settlements are frequently recognized by their wastes, Pollution was not a serious problem as long as there was enough space available for each individual or group. However, with the establishment of permanent settlements by great numbers of people, pollution became a problem, and it has remained one ever since.

By the middle of the 20th century, an awareness of the need to protect air, water, and land environments from pollution had developed among the general public. In particular, the publication in 1962 of Rachel Carson’s book Silent Spring focused attention on environmental damage caused by improper use of pesticides such as DDT. In response, major pieces of environmental law and regulation were passed in many countries to control the environmental pollution.

Great efforts are made to limit the release of harmful substances into the environment. Unfortunately, attempts at pollution control are surpassed by the scale of the problem, especially in less-developed countries. Noxious levels of air pollution are common in large cities. To control the pollution completely, we still have a long way to go.

4 . Microplastics, or tiny plastic particles - have been found in human blood for the first time.

In a paper published in Environment International, researchers in the Netherlands analyzed 22 blood samples from healthy donors and found that 17 or almost 80% contain microplastics.

The team tested for five types of plastics. Polyethylene terephthalate (PET), commonly used in disposable water bottles, was the most common plastic type and found in about 50 percent of the donors. The second most common, polystyrene (PS) which is used for food packaging, was found in about 36 percent. Alarmingly, the researchers found up to three different types of plastic in a single blood sample.

Previously, microplastic pollution has been recorded to the summit of Mount Everest, oceans, seafood, water and air. It is the first study to find such tiny particles in human blood. “The particles are transported throughout the body and stay in internal organs,” study author Dick Vethaak, an ecotoxicologist in the Netherlands says to the Guardian.

The health effects of taking in microplastics are currently unclear. Today, the only data available are laboratory studies that show its unfavorable effects on mice or rats when given large quantities of microplastics. As Professor Mark Taylor of Macquarie University in Sydney told The Guardian last year, “nobody really knows.” However, as he stressed., “Absence of evidence is not evidence of absence.” If we’re to understand the effects, the first step underway at the moment is understanding levels of exposure.

It is estimated that since the 1950s, more than 70 million tons of microplastics have been dumped into the oceans due to industrial manufacturing processes. A WWF report also suggested we’re all unintentionally taking in 125 grams of plastic every 6 months. Despite the small number of donors in the study, pollution expert Fay Couceiro of the University of Portsmouth, who was not involved in the study, tells the AFP that the study was “solid and will stand up to examination.” Now, many countries are taking action to reduce microplastics in the environment.

5 . Most cities were built on rivers. People originally settled in Paris because of the Seine, and in London for the Thames. A third of New York City’s surface area is water. For centuries, city folk used rivers for shipping, fishing and play. In a rare city without a big river, Johannesburg say, you notice its absence.

Yet in recent decades, we have ignored urban rivers. The Industrial Revolution ruined rivers for more than a century. Huge new urban populations filled them with waste water, factory emissions(排放物) and harmful gases of ships. In Newcastle in the early 1800s, salmon(鲢鱼) had been so plentiful in the River Tyne that apprentices(学徒) were said to have terms in their contracts stating that their masters shouldn’t make them at it every day. By the 1950s, the salmon were gone.

However, in recent decades, cities began cleaning up rivers. The Thames is now the cleanest it has been in 150 years and has seals and the occasional whale, sometimes alive. In cities like Chicago, riverside storehouses have been turned into fashionable restaurants and waterfront apartments. All in all, the latest trend is to change urban waterways into the natural play space so lacking in most cities.

But rivers also need to regain their original purpose as transport center. Passenger traffic may decrease as an urban issue if working from home becomes the norm during and even alter the pandemic. But there’s one form of urban traffic that just keeps growing: deliveries. Imagine using the enormous capacity of shipping to take delivery trucks off the roads. One of the newer Thames barges(驳船) with a capacity of 1, 750 tons can replace 44 large trucks, which uses much less energy and causes less noise pollution. In other words, we need to turn truck drivers into barge captains.

Rivers are the reason our cities are where they are. We just forgot about them.