Leipert, C. (1989). National Income and Economic Growth: The Conceptual Side of Defensive Expenditures. Journal of Economic Issues 23(3), 843–856.
Leipert defines defensive expenditures as outlays that compensate for or prevent the harmful effects of production and consumption: pollution control, the health costs of environmental damage, longer commutes and security among them. Because the national accounts book these as final output, a rising share of them inflates measured growth without adding to welfare. The wiki cites the article for the defensive-spending mechanism in What GDP Leaves Out, and records there that no current estimate of its size was found.