Reductions in Zn, Cu, and Pb concentrations can be clearly seen
in all three cores from the end of the 1990s to the present time
(Fig. 2), despite increases in population and in economic activity
(Fig. 3). In the 1990s, with the aim of protecting the natural environment
and the health of its citizens, the Philippines government
introduced a new law for environmental management, Administrative
Order No. 42 (Global Environmental Forum, 1997). This new
law introduced stricter environmental regulation of water quality,
air pollution, and industrial wastes, and provided a more severe
punishment of polluters than did the previous version. It also abolished
the use of leaded gasoline throughout the country. The sharp
declines in Zn and Cu, as well as Pb, concentrations in the sediment
cores reflect the results of the enforcement of Administrative Order
No. 42 in the 1990s (Figs. 2 and 3). It can therefore be concluded
unequivocally that the rate of decline in heavy metal pollution increased
dramatically from the end of the 1990s due to stricter
environmental regulations being enforced by the Philippines
government