What was the Summers memo of 1991 sarcastic about?
The context of this memo was an emerging debate about structural adjustment and its environmental implications. The World Bank has attached a wide range of liberalization policies to many of its loans. These policies were meant to increase trade and foreign investment and to decrease fiscal deficits, all of which should help countries to pay back their loans. Critics argue that imposing these forms of liberalization on LDCs forces them to prioritize repayment over other policy goals, including environmental protection. 

Here is a 2003 review on environmental impacts of structural adjustment by Bank researchers which briefly mentions and dismisses the "pollution haven... hypothesis that 'dirty' industries migrate to low-income countries after trade liberalization because of differences in costs of pollution abatement and looser environmental standards (p. 27)."