[4] It is called genetic pollution when it negatively impacts the fitness of a population, such as through outbreeding depression and the introduction of unwanted phenotypes which can lead to extinction.
One such example is the introduction of the Asian Longhorned beetle in North America, which was first detected in 1996 in Brooklyn, New York.
The beetles are highly damaging to the environment, and are estimated to cause risk to 35% of urban trees, excluding natural forests.
Tomás Carlo and Jason Gleditch of Penn State University found that the number of "invasive" honeysuckle plants in the area correlated with the number and diversity of the birds in the Happy Valley Region of Pennsylvania, suggesting introduced honeysuckle plants and birds formed a mutually beneficial relationship.
Invasive species can cause extinctions of small populations on islands that are particularly vulnerable due to their smaller amounts of genetic diversity.
In these populations, local adaptations can be disrupted by the introduction of new genes that may not be as suitable for the small island environments.
The New York Times cites, from the words of biologist Luigi Boitani, "Although wolves and dogs have always lived in close contact in Italy and have presumably mated in the past, the newly worrisome element, in Dr. Boitani's opinion, is the increasing disparity in numbers, which suggests that interbreeding will become fairly common.
[12][13][14] Farming structures may be ineffective at holding the vast number of fast growing animals they house.
[15] Natural disasters, high tides, and other environmental occurrences can also trigger aquatic animal escapes.
"[20] A report done by that organization in 1999 did not find that escaped salmon posed a significant risk to wild populations.
The genetic make-ups of many crops is different from those of their wild relatives,[23] but the closer they grow to one another the more likely they are to share genes through pollen.
In the fields of agriculture, agroforestry and animal husbandry, genetic pollution is being used to describe gene flows between GE species and wild relatives.
[25] While intentional crossbreeding between two genetically distinct varieties is described as hybridization with the subsequent introgression of genes, Rifkin, who had played a leading role in the ethical debate for over a decade before, used genetic pollution to describe what he considered to be problems that might occur due to the unintentional process of (modernly) genetically modified organisms (GMOs) dispersing their genes into the natural environment by breeding with wild plants or animals.
[24][26][27] Concerns about negative consequences from gene flow between genetically engineered organisms and wild populations are valid.
Since 2005 there has existed a GM Contamination Register, launched for GeneWatch UK and Greenpeace International that records all incidents of intentional or accidental[31][32] release of organisms genetically modified using modern techniques.
[33] Genetic use restriction technologies (GURTs) were developed for the purpose of property protection, but could be beneficial in preventing the dispersal of transgenes.
Physical containment includes barriers such as filters in labs, screens in greenhouses, and isolation distances in the field.
[4] The genes of each population of the ibex in Turkey and Sinai were locally adapted to their environments so when placed in a new environmental context did not flourish.
Additionally, the environmental toll that may arise from the introduction of a new species may be so disruptive that the ecosystem is no longer able to sustain certain populations.
Gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.
[44] These environmentalist groups stand in complete opposition to the development and production of genetically engineered organisms.
Rhymer and Simberloff argue that these types of terms: ...imply either that hybrids are less fit than the parentals, which need not be the case, or that there is an inherent value in "pure" gene pools.