3 . I fell in love with rhinos when I worked in a zoo in the 80s, and spent much of the next 20 years as the keeper of the largest captive (圈养) group of rare black rhinos.

There’s a popular misconception that rhinos are aggressive and stupid, but I discovered sensitive, affectionate animals. Weighing over a ton, black rhinos are unexpectedly swift and have an unpredictable nature — but, given reassurance, they can be very trusting. In the past few decades, their numbers have dropped dramatically. In recent years, I’ve helped look after rhinos being moved to animal shelters, so they can form new populations in countries that have few left.

Last year, I helped on a project to fly five black rhinos from a private reserve in South Africa to the Serengeti National Park. Once there, the animals had to be kept captive for a few weeks to adapt to the new environment, in which time they lived in bomas — wooden enclosures (围场) with bedrooms, designed to create a calm space.

A couple of weeks before their planned release, the sky filled with smoke. Watching the flames rushing through the bush toward the bomas, I froze. Terrified that it would catch fire, my instinct was to release the rhinos, but they hadn’t yet been fitted with transmitters (信号传送器). If I let them out into a bushfire and they were injured, we’d have great difficulty tracking them down.

So I rushed back to the bomas and called the rhinos to the bedrooms. Sensing the fear in my voices, they moved without hesitation and remained astonishingly calm. It was crucial the rhinos didn’t panic — they can easily hurt each other if they do.

Meanwhile, the keepers managed to beat the closest flames away. At last, after half an hour, the wind changed direction and the fire began to die down.

That we and the rhinos had escaped uninjured was a miracle. The teamwork of everybody there played a large part, and the rhinos were very much a part of that team. The relationships we’d built with them had proved crucial — had they or we panicked, all our work would have been in vain. Instead, two weeks later, they were released into the wild, ready to found part of a new population in the Serengeti.

4 . It has always been assumed that noise is a problem unique to animals. But a new study by Dr. Ravandi, a botanist at Shahid Beheshti University in Tehran, has revealed that plants suffer too.

That plants can be affected indirectly by noise pollution has never been in doubt. What has remained unknown is whether or not plants themselves suffer directly from noise pollution.

Sounds are pressure waves transmitted (传播) through gases, liquids and solids. Scientists have previously assumed plants may be able to sense these waves as they are struck by them. A number of experiments have confirmed this in recent years — plants exposed to ultrasound in the lab have shown a range of negative responses including the expression of stress-related genes, slow growth and reduced seed development.

Yet exposing plants to ultrasound is not the same as growing them in the presence of actual traffic noise. To this end, Dr. Ravandi decided to set up an experiment to explore it.

Working with a team, Dr. Ravandi grew two species in his lab that are commonly found in urban environments — marigolds and sage. The plants, grown from seed and allowed to mature for two months in the same space, were divided into two groups. One group was exposed to 73 decibels (分贝) of traffic noise recorded from a busy motorway in Tehran for 16 hours a day. The other group was left to grow in silence. After 15 days had passed, samples were taken from the youngest fully expanded leaves on every plant in the experiment and studied.

None of the plants exposed to the traffic noise did well. Analysis of their leaves revealed all of them were suffering. Chemical compounds (化合物), such as hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) , are indicators of stress in plants and both were found at much higher levels in the plants exposed to the traffic noise. Most notably, malondialdehyde (MDA) levels in the sage plants exposed to noise were double what they were in those grown in silence and hydrogen peroxide (H₂O₂) levels were three times higher in marigolds grown with the noise than those grown in silence.

Dr. Ravandi’s findings make it clear that, though plants lack ears, the vibrations (震动) generated by the noise of traffic still bother them enough to give rise to dramatic stress responses that are not much different to those that would be found in plants exposed to drought, highly concentrated salt or heavy metals in their soil.

The question now arises whether all species are affected similarly by noise pollution. Nature is not silent. It remains a mystery if certain plant species have developed mechanisms to address noise pollution, which could potentially be transferred to urban plants in the future.

Thank you!

7 . In the rich countries of the West, the electric vehicle revolution is well occurring. Climate-conscious consumers drive Teslas or Polestars for reasons of morality (道德) and fashion. Poorer countries are also experiencing a wave of electrified trend. In Bangladesh, electric three-wheeler taxis, known as tuk-tuks, are rapidly replacing gas-powered ones on the streets. Such electric vehicles are climate friendly, cost effective, and help reduce air pollution.

Yet a glance under the hood (引擎盖) of these vehicles shows a poisonous secret: each tuk-tuk runs on five massive lead-acid batteries (铅酸电池), containing almost 300 pounds of lead (铅) in total. Every year and a half or so, when those batteries need to be replaced and recycled, about 60 pounds of lead leaks into the environment. Battery recycling, often at small-scale unregulated factories, is a highly profitable (高利润的) but deadly business.

Lead is dangerous, and any exposure to it is harmful to human health. Lead that has entered the environment hurts people on an unexpected scale. The numerous ways lead enters air, water, soil, and homes across the developing world and the enormous damage it does to human health, wealth, and welfare cause one of the biggest environmental problems in the world yet receives little attention.

The World Bank estimates that lead kills 5.5 million people per year, making it a bigger global killer than AIDS, malaria, diabetes, and road traffic deaths combined. On top of the shocking deaths, the social burden of lead poisoning is heavy, as is its contribution to global inequality — our research on the cognitive (认知的) effects of lead poisoning suggests that it may explain about one-fifth of the educational achievement gap between rich and poor countries.

But unlike many challenges faced by developing countries, lead poisoning is a problem that can be resolved through financial investment (财政投入). Better monitoring, research, and rules can help protect children all over the world from the unpleasant effects of lead poisoning and reduce the massive global costs it brings.

Thank you!