# Table S2
#
# The table shows the mean of (nominally) five replicates per laboratory 
# for each of eight elements in a reference material certification exercise. 
# NA denotes missing values; that is, the laboratory did
# not report results for the element concerned.
# All values are given in ug/L (micrograms per litre)
#
LabID	Arsenic	Cadmium	Chromium	Copper	Lead	Manganese	Nickel	Zinc
Lab1	10.014	5.0900	48.084	2016.0	25.290	50.632	19.740	613.44
Lab2	10.288	4.9880	48.166	1936.4	24.240	47.246	19.214	634.52
Lab3	10.166	4.9719	47.373	1682.4	22.893	48.073	18.525	598.21
Lab4	 9.096	4.4700	44.382	1882.2	21.202	44.310	19.568	551.14
Lab5	10.004	4.8880	49.654	1970.8	23.976	48.100	19.624	607.57
Lab6	10.440	4.9560	49.820	1900.0	22.560	48.700	18.520	654.20
Lab7	10.342	4.9220	50.368	1938.3	23.256	49.020	19.944	620.32
Lab8	10.474	4.8440	45.712	2068.2	23.670	46.668	20.616	625.04
Lab9	30.916	4.6120	44.742	1959.9	26.592	47.654	20.340	582.48
Lab10	10.120	3.9580	54.480	2048.0	19.060	51.620	   NaN	578.00
Lab11	10.700	4.9800	48.540	2013.8	26.520	45.300	19.880	626.06
Lab12	 9.876	4.8220	46.086	1827.1	23.780	48.072	18.740	608.12
Lab13	10.440	5.1020	51.160	2026.0	24.920	50.500	18.340	603.20
Lab14	10.412	4.8580	49.300	1845.2	22.494	47.460	18.288	554.12
Lab15	10.200	4.8960	48.960	1956.2	   NaN	48.376	19.528	   NaN
Lab16	 9.603	4.9120	47.108	2225.2	24.710	49.298	17.432	592.26
Lab17	 9.934	4.8220	50.520	2096.0	22.260	49.700	17.580	556.80
Lab18	10.502	4.8616	47.556	1830.5	22.870	46.106	19.528	597.31
Lab19	 9.942	4.8120	47.182	1686.8	24.706	43.656	19.184	556.13
Lab20	 9.534	4.9180	47.916	1803.7	24.950	53.564	20.032	564.96
Lab21	10.362	4.7042	51.594	2054.7	24.047	50.012	19.823	633.50
Lab22	10.314	4.9660	52.684	1938.2	23.550	49.774	20.840	586.24
Lab23	   NaN	6.0000	48.200	1886.0	30.000	47.800	 0.000	620.60
Lab24	10.180	4.8520	47.740	2040.0	23.040	46.720	19.320	   NaN
Lab25	10.054	4.9660	46.266	1893.2	24.262	51.548	19.628	590.62
Lab26	 9.794	5.2200	55.467	2019.0	23.160	51.945	21.162	663.69
Lab27	   NaN	   NaN	   NaN	1865.2	22.026	45.982	18.806	559.93
Lab28	 5.342	   NaN	45.660	1906.4	   NaN	40.862	   NaN	607.51
Lab29	12.420	6.0300	55.033	1888.7	30.013	50.173	19.977	589.88