Dakar, Senegal - The dusty air is filled with the sounds of car horns and shouting - "500 CFA [$0.80] for a pair of trousers!", "300 CFA [$0.50] for a T-shirt!" - from all directions as sellers try to entice customers to their stalls.

This kilometres-long stretch of road is home to a weekly market, where stalls are squeezed one next to another, selling an array of second-hand clothing in Dakar's Gueule Tapee neighbourhood for as far as the eye can see.

The second-hand clothing industry is big business in Senegal with an estimated 18,500 tonnes of used clothes imported each year. But concerns have been raised about the economic, ecological, and ethical repercussions of clothing donated to charities resulting in hundreds of millions of dollars in profits each year.

Used garments are everywhere here: there are thousands of trousers, bras, underpants, and tops piled onto carts and tables, spilling onto the ground.

A man dodging traffic masterfully holds four pairs of jeans over his arm, hopeful that he'll make a sale to a driver stuck in a traffic jam. Another wearing a "Nashville Walk for Lupus 2007" T-shirt hurries past a stall selling second-hand socks.

WATCH: Fair fashion (25:00)

The Waste & Resources Action Programme (WRAP), a UK government-backed agency tasked with reducing waste, estimates that more than 70 percent of all reused clothing in the UK ends up overseas. Among several other organisations sending second-hand clothes to Senegal is Frip Ethique, Oxfam's social enterprise in the country.

According to Oxfam, clothes donated in the UK are sorted by volunteers and, where possible, sold in their shops.

However, Andrew Brooks, a lecturer of development geography at King's College London, argues in his book Clothing Poverty: The Hidden World of Fast Fashion and Second-hand Clothes, that as few as 10-30 percent of charity donations are actually sold over the counter, with similar numbers also indicated in Canada and the United States.

'Everything gets sold'

Frip Ethique imports more than 2,500 tonnes of donated clothes to Senegal annually. Shipments arrive from the UK several times a month, and the clothes are sorted by employees into 45kg bales according to type.

The bundles are then brought to Frip Ethique's wholesale store in Colobane, a Dakar neighbourhood known for its second-hand clothing trade, where vendors can buy the bales to be sold at market stalls, one item at a time. Vendors have no choice but to buy the bales as a whole, only knowing what type of clothing they are purchasing, with no idea of the style or quality of the items.

"Everything gets sold. The items that can't be worn will be sold as cloth to factories and garages," says Mouhamadou Konte, operations manager at Frip Ethique.

"The clothes are already sorted in the UK, they send us what we call a 'light tropical mix', suitable for the climate here. But sometimes [unsuitable] items slip through, it's inevitable," he says, picking up a child's woollen mitten off the floor.

Ten years ago, the quality of clothing was a lot better, says Amy Gueye, stock manager at Frip Ethique.

"We try to sell everything, but there are a lot of bales that won't be sold," says Gueye, pointing at dozens of bundles stacked against the wall.

"In Senegal, women are very particular about fashion; they tend to wear dresses and skirts, rather than T-shirts. Trousers sell well - as do women's and men's underwear."

Although charities are not purposefully deceitful about what happens to clothing donations, there seems to be a disconnect between what consumers think happens to their used outfits - many are unaware that the items are sold overseas, turning charitable donations into multi-million dollar profits.

According to UN figures, the UK is the second largest used clothing exporter after the US. In 2015, it exported more than 321,500 tonnes of clothing worth about $563m overseas. The top destinations were Pakistan, Angola and India.

The issues surrounding donated clothing are multi-faceted.

Although it provides a steady livelihood for thousands of people, the sector is largely unregulated and highly vulnerable to illicit trading. In Colobane, where a lot of the bales of clothes are sold, not a single wholesaler agreed to talk to Al Jazeera.

The vastness of the second-hand clothing industry also raises questions about the Western charity mentality: how would you feel wearing someone else's used underwear?

As well as social, ethical and economic issues, the multi-million dollar trade also has environmental impacts.

Walking along the Senegalese shoreline, the magnitude of the issue is discernible: bits of used clothes are tangled up with plastic bags and fishing nets, washed ashore with each incoming wave.

In Ziguinchor, 270km from Dakar, in the southern region of Casamance, the effects are visible on the delicate ecosystem of the mangroves.

"Working in the Casamance mangroves for the past few years, I have observed the impact of waste related to clothing. In Ziguinchor, in particular, the Mandinka and Joola communities refrain from burning children's clothes," says Octavio Fleury from Oceanium Dakar, an environmental protection organisation.

"They have two solutions: burying them under a termite mound or throwing them into the sea, and that is how we end up with mounds of clothes in the mangroves … But the sea is not a bin and neither is the mangrove."

With the quantities of imported used textiles, the effects on the local clothing industry are also tangible.

In 2016, Burundi, Kenya, Rwanda, Tanzania and Uganda announced a plan to ban imports of second-hand clothes by 2019.

Senegal is slowly beginning to resuscitate its once-booming textile industry. More than $425m has been invested in the country's largest textile factory based in Thies, about 50km west of Dakar, which closed its doors more than 15 years ago.

But with second-hand clothing available at a fraction of the price, it remains to be seen whether the revival of the local textile industry will be successful without strict government quotas on imports.