Rachel Carson knew Clarence Cottam, Assistant Director of the U.S. Fish and Wildlife Service (USFWS) and an active researcher. Cottam and Elmer Higgins, Chief of the Division of Fishery Biology at USFWS published a monograph in 1946 on the harms of the then-new insecticide DDT, with suggestions on how to use it more safely. It was an early publication from USFWS, indicated by the title, Circular 11.
This was one of the earliest publications to document harms from DDT across the spectrum of DDT use and the spectrum of wildlife.
Finding the publication in libraries now is difficult. Funding cuts at many libraries encouraged them to throw away materials not heavily used, and this one was not the most popular in most libraries who may have had it.
So when I ran into a .pdf of the circular on a NOAA site, I downloaded it, and I make it available to you here.
In the introduction Cottam and Higgins explain why the monograph was published:
Most organic and mineral poisons are specific to a degree; they do not strike the innumerable animal and plant species with equal effectiveness; if these poisons did, the advantage of control of undesirable species would be more than offset by the detriment to desirable and beneficial forms. DDT is no exception to this rule. Certainly such an effective poison will destroy some beneficial insects, fishes, and wildlife.
The circular said when DDT was used, deaths resulted in mammals, amphibians, birds and fish.
DDT history revisionists are fond now of saying DDT is “harmless” and “safe.” This 1946 publication makes clear that neither is true. While it may take a large dose to cause acute harm to large mammals, like cattle and humans, it is quite deadly to smaller wildlife in all branches.
Cottam and Higgins recommended caution, reducing does of DDT in use, and careful monitoring after use.
Use DDT only where it is needed. Wherever it is applied by airplane, provide careful plane-to-ground control to insure even cover–age and to prevent local overdosage.
In forest-pest control, wherever feasible, leave strips untreated at the first application to serve as undisturbed sanctuaries for wildlife, treating these strips at a later time or in succeeding seasons if necessary.
In the control of early appearing insect pests, apply DDT, if possible, just before the emergence of leaves and the main spring migration of birds; for late appearing pests, delay applications, whenever practicable, past the nesting period of birds. Adjust crop applications and mosquito-control applications so far as possible to avoid the nesting period.
Because of the sensitivity of fishes and crabs to DDT, avoid as far as possible direct application to streams, lakes, and coastal bays.
Wherever DDT is used, make careful before and after observations of mammals, birds, fishes, and other wildlife.
Wildlife scientists were not working blind with DDT after 1946.