While many environmental contaminants degrade quickly in the environment, others (Buccini 2004):

  • Are released in quantities, concentrations or under conditions so that elevated concentrations are sustained in the environment; and
  • Have a combination of physical and chemical properties so that, once released to the environment, they degrade very slowly and remain present in the environment and organisms for many years or even decades, even when released in relatively small quantities. These chemicals are said to be persistent.
Box 5: Impacts of chemicals on fish catch and wetlands in Senegal

Water pollution by biomedical waste and agricultural and industrial chemicals affects wetlands and favours invasion of these areas by invasive species such as Typha and Salvinia molesta. The potential of Senegalese fisheries resources is decreasing significantly due to the destruction of the plankton by chemicals released by agricultural and industrial sectors. This has resulted in a continuous decrease in the catches and a loss of quality. From 1969 to 1988, official catches decreased from 20 000 to 8 000 tonnes.

Source: CSE 1999

Persistent chemicals can, through natural environmental processes, be distributed over long distances, leading to regional and global contamination (Buccini 2004). Many of these enter the food chain and are retained in organisms at concentrations higher than those in food and water – a process known as biomagnification. These substances are said to be bioaccumulative. In recent decades, there has been increased attention paid to addressing the risks posed by substances that are persistent, bioaccumulative and toxic (PBT), POPs and some metal compounds. However, many other chemicals, thought to be less harmful, are having significant negative impacts on biodiversity and human health (WWF 2004a).

Chemical pollution compromises the integrity of ecosystems, and thus directly threatens biodiversity. The increased discharge of nitrogen compounds from fertilizers in rivers can result in the eutrophication of surface and coastal seawater, and, in extreme cases, a state of complete oxygen depletion (anoxia) which severely affects the ecosystem and results in fish deaths. Excessive use of chemical fertilizers also contributes to the degradation of land through salinization, thus limiting agricultural production potential.

Chemicals pose many threats to wildlife. Research over many decades has demonstrated the adverse and often irreversible effects of POPs, PCBs, and heavy metals on the endocrine systems, especially reproductive hormones (WWF 2004a). These disruptions are now understood to have much more extensive effects including on thyroid and pituitary systems. Neurological damage is a common feature of chemical poisoning and many chemicals are carcinogenic. With the increase in chemical use these impacts on wild animals have increased (WWF 2004b). Chemicals previously thought to be safe, but with negative impacts on wildlife include (WWF 2004a):

  • Perfluroocatanes – these are widely used as surfactants and emulsifiers. They are used as water protectors for carpets, textiles, leather, food packaging and other containers. They are also used in the production of shampoo and dental cleaners, and as lubricants for bicycles, tools and zips.
  • Phtalates – this group of chemicals are used as softeners in a variety of plastic products including in medical equipment, building products, car products, upholstery, clothing and children’s toys.
  • Phenols – these are used in the production of polycarbonate plastics that are widely used in electrical appliances.
  • Polybrominated flame retardants – these are widely used in furniture, building materials and clothing.

Increasing human consumption and poor waste management are key factors in this growing threat to biodiversity.