In 2009 Denise McAlooyse and Alisa Newton published a paper in Nature Reviews Cancer highlighting the issue of wildlife cancers and pointed out that human activities contribute to these cancers. Researchers undertaking studies into the Beluga whale cancer in the St Lawrence estuary have also queried if pollution is causing these cancers.
My focus has been the Tasmanian devil cancer but three other wildlife cancers threaten sub-populations of the California sea lion in the San Francisco Bay, the Beluga whale in the St Lawrence Estuary and the Green sea turtle in Moreton Bay, Queensland.
There is an urgent need for toxicology studies that thoroughly assess the hazards posed by synthetic chemicals in the environment to wildlife acting as bio-indicators to human health. Studies that not only investigate the role of toxins individually but synergistically (together) within complex ecosystems.
Early research by Rachel Carson and Theo Colburn and her colleagues raised the issue of chemicals that act as endocrine disrupters, which cause harm at critical points in the development of an organism. These endocrine or hormone disrupting chemicals are linked to many modern chronic diseases including diabetes, obesity and cancers as well as developmental and reproductive disorders and cancers.
A more recent development is the study of epigenetics and the role of chemicals in inter-generational genetic changes. These changes are passed from parent to offspring and are implicated in the development of chronic diseases such as cancer.
California sea lion
The predominant cancer in California sea lions in both sexes is a urogenital (urinary tract) carcinoma which is epithelial (skin). The cancer was first discovered in a group of sea lions on Pier 33 near Fisherman's Whaft in the San Francisco Bay. The Gulf of California is heavily polluted and from the late 1940s until the early 1970s millions of pounds of DDTs and polychlorinated biphenyls (PCBs) were discharged into the sea.
St Lawrence Estuary Beluga whales
In 2002 Daniel Martineau and others carried out a study of Beluga whale carcasses reported stranded between 1983 and 1999. They found cancer as the major cause of death (a cancer of the intestine was identified in 30% of the whales). The rate is higher than that for any other wild mammal species. Cancers detected also included mammary gland cancer - a first for marine mammals. This type of cancer is rare but it is etiologically associated with the ingestion of herbicides. The St Lawrence Centre studies revealed that of the twenty-two pesticides monitored in the St Lawrence River atrazine and metolachlor were the most frequently detected (in 85% and 68% of samples analysed respectively) and at the highest concentrations.
Green sea turtles
Green sea turtle populations inhabiting Florida, Hawaii, the Caribbean and Moreton Bay, Queensland are known to have a cancer. The cancer in the Green sea turtles in Moreton Bay has been described as an epithelial (skin) fibropapilloma. The tumours grow primarily on the skin and most often around the neck and shoulders. A worldwide feature of the habitats where Green sea turtle cancer is found is contaminated by industrial, agricultural and urban pollution. Moreton Bay is significanly contaminated. Seagrass declines in Moreton Bay have been attributed to the worsening water quality due to an increase in contaminants and toxins. Moreton Bay catchment includes 14 major river catchments and 6 drainage basins including the Pine River, Maroochy River and Noosa River. Chemicals detected in the Noosa River include atrazine, endosulfan sulphate, trichlorfon, and carbendazim. All are endocrine disrupters which interfere at critical times in reproductive and developmental processes in living organisms at extremely low levels (parts per billion).