Some studies that have highlighted the turning points of the EKC for water pollution are mentioned below:
Lee at al (2009) studied a broad sample of 99 countries for 1980 -2001 to test the EKC hypothesis between real income and BOD. The study found evidence of an EKC in America and Europe with turning points of approximately $ 13,956 and $38,221 respectively. However, no evidence of an EKC was found for developing countries in Africa, Asia and Oceania. The study makes a useful comparative insight between developed and developing countries. The study strongly supports the theory of regional differences in EKC.
Grossman and Krueger (1995) found that turning points vary with the pollutants but in general occur at a per capita of less than USD 8000 for all contaminants (including BOD).
Solakoglu (2007) assessed the change in environmental quality ( BOD and TSS were proxies for water pollution ) of EU- member and non-EU member countries from 1987- 2000.EU member transition with well-defined property rights validated the EKC with a turning point of USD 5,710 while no EKC was found for non-EU members who had poorly defined property rights.