Mercury

Toxicity to soil microorganisms

Description of key information

On the basis of the EC values from studies with microorganisms, varying from 1.5 (ATP content, Zelles et al, 1985) to 2000 mg/kg d.w. (phosphatase activity, Tyler, 1981) NOEC values in standard soil vary from 1.4 to 2406 mg/kg dw). The lowest NOEC for inorganic mercury in micro-organisms is 1400 µg/kg d.w. (Zelles et al, 1985, standard soil). 

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

1.4 mg/kg soil dw

Additional information

Eight reliable and relevant studies were identified with data from multiple micro-organisms, discussed in the Dutch Basic document for mercury. The influence of inorganic mercury on microbial activity in different soil types was measured (Slooff et al, 1995). Due to the short generation time of microorganisms no selection has taken place based on test duration; results from short-term tests are also considered relevant. Parameters studied were: carbon mineralisation, nitrogen mineralisation, enzyme activities (amylase invertase, phosphatase, urease-, ATP-content and H2-oxydation. The NOEC’s were standardised to values for standard soil for the purposes of PNEC derivation: the NOEC was calculated from the EC values by using an assessment factor of 2 to 10. Natural soils used in ecotoxicological tests differ in characteristics such as organic matter and clay content, soil pH, cation exchange capacity (CEC) and soil moisture content. Natural soil tests can also be used in terrestrial tests, especially in higher tier tests. The results from these natural tests can be converted to a standard soil, which is defined as a soil with an organic matter content of 3.4%

Species	Trophic level	Hg-salt		Effect parameter	Value (mg Hg/kg dry wt)	Klimisch score	Reference
Microorganism	Microorganisms	HgCl2	Nominal	3d- NOECrespiration (Sandy loam) 3d- NOECamylase activity (Sandy loam)	79 79	K2 K2	Tu, 1988
	Microorganisms	HgCl2	Nominal	28d- NOECrespiration (Arvada) 28d- NOECrespiration (Bainville) 28d- NOECrespiration (Terry) 6h- NOECrespiration (Arvada) 6h- NOECrespiration (Campspass and bainville) 6h- NOECrespiration (Heldt) 6h- NOECrespiration (Terry)	9 99 124 35 40 208 248	K2 K2 K2 K2 K2 K2 K2	Landa and Fang, 1978
	Microorganisms	HgCl2	Nominal	28d- NOECrespiration (Litter)	12	K2	Spalding, 1979
	Microorganisms	HgCl2	Nominal	1d- NOECrespiration (clay)	31	K2	Pancholy et al, 1975
	Microorganism	HgCl2	Nominal	42d- NOECammonification (clay) 42d- NOECnitrification (clay) 42d- NOECammonification (sand) 42d- NOECnitrification (sand)	6 10 6 10	K2 K2 K2 K2	Van Faassen, 1973
	Microorganisms	HgCl2	Nominal	3h- NOECfosfatase activity (spar-mor)	2406	K2	Tyler, 1981
	Microorganisms	HgCl2	Nominal	1,5h- NOECfosfatase activity (alkalic)(Okoboji)	456	K2	Juma and Tabatabai, 1977
	Microorganisms	HgCl2	Nominal	48d- NOECATP-content (agr. soil)	1.4	K2	Zelles et al, 1985