Murihiku – our story

In New Zealand, the use of Dichloro-diphenyl-trichloroethane, or DDT, was mostly in fighting the agricultural pests grassgrub (pictured) and porina caterpillars.

IF you are of the older generation, then DDT will be a familiar sequence of letters.

It stands for Dichloro-diphenyl-trichloroethane.

When I was a kid my father had a small puffer bottle of the powder for domestic purposes – keeping booklice out of the pressed plant collection, killing the silverfish that ate his books and eliminating the carpet beetles that chewed our rug.

I still see that little eruption of powder when I open one of his old books.

No doubt it’s still working on the silverfish.

I haven’t seen a silverfish in Invercargill although, when I was at the museum, we had the silverfish award, presented for inglorious contributions to conservation such as the dropped vase, the rat in the wedding dress and the ink spilt on the ancient manuscript.

DDT is a very effective insecticide developed in the 1870s. It was used in the fight against lice, mosquitoes, locusts and tsetse flies which spread sleeping sickness.

In New Zealand, its use was mostly in fighting the agricultural pests grassgrub and porina caterpillars.

There are several species of each, ironically native.

We do have native plants and animals that have become pests where favourable habitats and plentiful food has led to a population boom.

There is a wood pigeon or kereru infestation in my plum trees.

One plum last season! One! It was a greengage.

The use of DDT increased hugely in the United States after the war.

The population of Naples was dusted and the typhus epidemic ended when the lice died.

It was the new wonder treatment for insect pests, although, even in those days, there was concern about its effects as it was known to kill off beehives and remove beneficial insects.

The increasing evidence of a serious effect on the environment led Rachel Carson to publish her famous book, Silent Spring, in 1962.

The story she told was of a toxin that stayed in the food chain, accumulating in the top carnivores such as hawks, wolves and eagles, leading to sickness and death. Humans accumulated it as well.

The pesticide industry fought back, much as the tobacco industry had been doing, but the evidence was too great to ignore.

DDT was progressively abandoned throughout the world, with the US banning it in 1972, the UK in 1984 and New Zealand outlawing its use in 1988. The problem did not end there for two reasons.

Firstly, without an alternative to DDT, pest control programmes started to fail. Malaria and locust plagues returned.

The second problem was DDT was still in the food chain and the soil.

With a half-life of 2-15 years, it wasn’t going to vanish quickly.

The Mapua factory, where it had been made, closed in 1988 and there was a massive decontamination programme.

Throughout the country, including in Southland, unwanted stocks of DDT were dumped and, as erosion exposes these old dumpsites, there is concern the chemical will re-enter the environment.

Erosion of the coastal road to Colac Bay is an example of a potential DDT site reappearing.