DDT's toxic legacy haunts Zambezi Valley

Five decades after Zimbabwe defied international regulations by continuing to use the pesticide Dichlorodiphenyltrichloroethane (DDT), alarming signs of ecological and human health damage are emerging - most notably in the Zambezi Valley, one of the country's most vital ecosystems.

Among the most disturbing developments is the detection of DDT traces in the breast milk of women living in Nyamhunga, a densely populated suburb in the lakeside town of Kariba. This discovery underscores growing fears about the long-term impact of the pesticide on public health, particularly among vulnerable groups.

Despite global consensus on the dangers of DDT - culminating in bans across much of the world - Zimbabwe persisted with its use of the chemical for mosquito and tsetse fly control, citing its affordability and efficacy. While the country formally banned DDT in agriculture in 2001, its application for public health purposes, particularly malaria control, continues under strict regulation.

Health officials in Kariba have launched investigations into DDT's health impact, using breast milk sampling as an alternative method to autopsies and biopsies for detecting pesticide residues in human tissue. Though the initial findings are inconclusive, further testing is underway.

Historical records show the extent of Zimbabwe's reliance on DDT. The Ministry of Health and Child Care, along with the Tsetse and Trypanosomiasis Control Branch under the Ministry of Lands, Agriculture, Fisheries, Water and Rural Development, began using chlorinated hydrocarbons like DDT in the late 1960s. Between 1978 and 1989, DDT use averaged 200 tons per year, peaking at 442 tons in 1986. By 1990, over 68,000 square kilometres - mainly in the Zambezi Valley - had been treated with DDT, with some areas sprayed more than a dozen times.

Ecological methods, including clearing riverine vegetation and targeting wildlife hosts, have been used alongside chemical treatments to manage tsetse fly populations. However, the long-term environmental toll has been staggering.

Dr. Lightone Marufu, an aquatic ecologist at the University of Zimbabwe's Lake Kariba Research Station, highlighted DDT's far-reaching impact on local biodiversity. "DDT can cause thinning of eggshells in birds of prey and crocodiles, possibly leading to reproductive failures and biodiversity losses," he said.

Evidence of this damage is mounting. A study on African Goshawks revealed significant population declines in areas where DDT was applied. Similarly, fish sampled from Lake Kariba showed elevated DDT residues, with implications for both wildlife and the communities that rely on fishing for livelihood and nutrition.

"DDT disrupts sex hormone function, which affects reproductive health across species," Dr. Marufu added.

The Zimbabwe Parks and Wildlife Management Authority also reported a sharp decline in woodland bird populations in DDT-treated areas. Of 22 bird species monitored, eight showed significantly lower numbers - underscoring the pesticide's widespread ecological effects.

Despite the known risks, DDT remains in limited use for vector control. Officials at the Blair Research Laboratory noted that alternatives are available, though their long-term effectiveness remains under review due to concerns over developing pest resistance.

Dr. Marufu believes future efforts must include environmental cleanup initiatives such as bioremediation to remove or neutralize DDT from soil and water systems. "There's a great need for environmentally friendly pest control methods," he said. "But this requires partnerships, stakeholder cooperation, and policy shifts that prioritize both human and ecosystem health."

As Zimbabwe confronts the unintended consequences of its historical reliance on DDT, the balance between public health and environmental sustainability hangs in the balance. Without urgent intervention and strategic policy reform, the cost of DDT may continue to be paid by future generations and the fragile ecosystems they depend on.