Year	metric tons
1970	0
1971	0
1972	0
1973	1
1974	1
1975	1
1976	1
1977	1
1978	1
1979	1
1980	1
1981	2
1982	2
1983	2
1984	2
1985	2
1986	2
1987	2
1988	2
1989	2
1990	2
1991	2
1992	3
1993	3
1994	3
1995	3
1996	3
1997	3
1998	3
1999	3
2000	3
2001	3
2002	3
2003	3
2004	3
2005	2
2006	1
2007	1
2008	1
2009	1
2010	1
2011	1
2012	1
2013	1
2014	1
2015	1
2016	1