Conditions may change over time and conclusions should be interpreted in light of the latest available information. Irrigation from the Ord River in Western Australia's East Kimberley is planned to be extended, but concerns have been raised about possible soil contamination caused by exploration and drilling at the Sorby Hills lead deposit in the 1970s and 1980s. Results showed that most of the alluvial plain contains about 20 mg Pb/kg in the plant root zone, which is normal for Australian soils.
As it may involve adjacent areas, a sampling program (eg using Australian Standard AS 4482.1) should be designed to determine the extent. If clay is imported to line and seal the proposed channels and drains and is taken from near the Sorby Hills mineralized area, it should be checked for possible elevated lead.
Introduction
- Location of study area
- Sorby Hills lead deposit
- Irrigation area
- Consultation
- Lead in the environment
- Plant and lead interactions
- Lead concentrations and public health
Extensive percussive and diamond core drilling was conducted to determine the size and extent of the deposits. In 1978 an adit (steep mine entrance) was started to enter one of the pods to obtain better samples and information on the style of mineralization. The Pb-Zn-Ag mineralization at Sorby Hills occurs on the margin of the Bonaparte Basin adjacent to the northeastern edge of the Kimberley Block.
There are limited outcrops of the Button Formation and Burt Range Formation, both of which host mineralization flanking the basement rocks. Much of the lead in cities comes from motor vehicles using leaded gasoline (before 1986).
Methods
Sampling
The geographical location of sample sites, and the depth at which samples were taken, are in Appendix 4. As the only high lead value recorded in surface soils in the study area was from where mine spoil was spread on a road, approximately 10 of the surface samples were taken from such locations near the exploration site to explore this phenomenon. Samples were pooled from 0-5 cm depth at four to five locations within 2-3 m of each site.
Excavation pits were excavated to a depth of 200 cm and all but the surface and deepest samples were taken from the pit wall. Surface samples were collected using a new steel mini-pole and placed in a clean plastic container before being transferred to sample bags.
Analysis
Any visible soil particles remaining on the mini-pick or in the plastic container were brush cleaned prior to sampling. In addition, the sample ID was written on two small paper labels, one of which was in each bag. These were reduced to less than 3 mm prior to sub-sampling and, where relevant, grinding and digestion.
Since these analyzes were to determine the total lead in the sample, regardless of whether it is in the soil or coarse fragments, it is completely consistent. The only samples with significant coarse fragments were several from the adit road and vicinity.
Results
Sample characteristics
Lead concentrations
As the number of samples for each zone was small, they had to be pooled for further evaluation. Sites near limestone hills were consistently larger and more variable than the rest of the alluvial plain by a factor of two to five. Plots of lead levels indicate a halo extending east of the hills, shown in Figure 9.
The lead in the soil profile is variable in this area, but always higher than in the rest of the plain (Figure 10). The data in Table 4 suggest that there may be more lead with depth for sites near the limestone mounds. In contrast, there was no trend for increasing lead with depth for the locations of the rest of the plain where all values are well below 50 mg/kg.
A series of analyzes showed that the probability of >300 mg Pb/kg in the. Even if the top 95% values were used instead of the average, the probability would be less than 1%. The chance that a value above 300 mg Pb/kg will be found in the surface near the limestone hills is therefore very small.
The surface (and underground) samples for the rest of the plain all had values below 50 mg/kg and averaged less than 20 mg/kg throughout. Since the data for the sites near the limestone hill suggested that the probability of a value greater than 300 mg/kg was very low, the. The acid samples were mostly from the western edge of the plain, along the alignment of the cutoff drain.
Discussion
Seyfried MS, Wilcox BP (2006 ) Soil water storage and rooting depth: key factors controlling recharge in rangeland soils. Stone LR, Goodrum DE, Jaafar MN, Khan AH (2001) Rooting front and water depletion depths in grain sorghum and sunflower. Zaongo CGL, Hossner LR, Wendt CW (1994 ) Root distribution, water use and nutrient uptake of wheat millet and sorghum on West African soils.
Appendices
Pb values, although examination of the histogram in Figure A2a suggests that the frequency is skewed to the left. Using the upper 95% confidence limit for both the mean and standard deviation of the adjusted normal distribution, the probability of Pb>300 (log10 0Pb>2.477) becomes 0.127%. b) Due to the slightly skewed distribution of the log10 Pb values in (a), a second selection was made from 31 sites in what can be considered a high-risk area (Figure A1b), which includes all sites in (a) . Using the upper 95% confidence limit for both the mean and standard deviation of the fitted normal distribution, the probability of Pb>300 (log10 Pb>2.477) becomes 0.382%. b) Selected points in red Figure A1: Locations included in probability calculation.
The email requested a review of a report titled "Soil Lead (Pb) Concentrations in the Sorby Hills Area of the Proposed M2 Irrigation Area, East Kimberley." To investigate the concentrations of lead (chemical symbol Pb) in soils within the proposed irrigation areas of the Pb mineralized area near Sorby Hills, East Kimberley. In order to determine whether health problems are likely to arise if the development plan for the M2 area of the Ord Irrigation Area expansion goes ahead.
This includes blind repeat samples and wash blanks collected in the field that are sent to the primary laboratory to determine the precision of the field sampling and laboratory analysis program. Split samples collected in the field should be analyzed in a secondary laboratory to determine the accuracy of the analysis programs." There are also no details in the report on hygiene and cleaning of sampling equipment.
There are no details in the analytical methods of using QA/QC procedures. Some information on these issues should be provided in the report to assure the reader that appropriate laboratory QA/QC has been undertaken. There is very little of the area potentially contaminated by Pb, and the small areas of high concentration can be further delineated by a more targeted sampling and analysis program around the areas disturbed by the exploration and mining activities.
The real risks to agriculture that are of concern are not detailed in the preamble to the report. Plants do not readily absorb Pb from soil (McLaughlin et al. 1996) and Pb is not readily translocated from roots to shoots and fruits (Wolnik et al. 1983), so when elevated Pb concentrations are found in crops, they are often resulting from to surface contamination of the product by dust.
Location of surface soil samples collected by Peter McCosker (2001)
Chemistry Centre (WA) Analysis Report, 2001
Root depth under irrigation references
In order to optimize irrigation systems, soil samples were removed from the root zone of a citrus grove in Minas Geraisl, to a depth of 1.5 m Orange USA Paramasivamet al Within the text 0.9 m mentioned as the usual root depth. In deep soil the taproot descends to a depth of 20 feet, and the abundant, widespread feeder roots send down many anchor roots which penetrate several feet.
Location of sample sites in this study
Chemistry Centre (WA) Analysis Reports, 2007
Statistical analysis of results for near limestone hills
Review of draft report by Prof Mike McLaughlin
This review was initiated by the Department of Agriculture and Food, WA, in an email dated 11 October 2007. The report details the results of a field soil sampling program in the Ord Irrigation Area Extension and associated laboratory analyzes for total lead (Pb) concentrations. One quality assurance (QA) feature I would prefer to see would be regular "field duplicates" - where a field sample is homogenized in the field and split into two identical samples for analysis in the lab.
Note that the referenced Australian Standard was updated in 2005 (Australian Standard AS Guide to the Investigation and Sampling of Potentially Contaminated Soil Sites.. Volatile and Semi-Volatile Compounds). Some information on these issues should be provided in the report to assure the reader that appropriate quality control (QC) and QA were performed during sampling. The Australian National Environmental Protection Agency (Assessment of Site Contamination), Schedule B3, Guideline on Laboratory Analysis of Potentially Contaminated Soils describes laboratory QA/QC procedures recommended for potentially contaminated sites.
At a minimum, certified reference material should have been analyzed and the results reported to ensure analytical accuracy for Pb. No data was presented for soil pH and EC, but these were indicated as analyzed on the soil samples. Since Pb availability to crops in soil is related to soil pH (Koeppe 1977; Reddy and Patrick 1977), these data, if the soil is neutral to alkaline, can provide additional assurance that availability of any Pb to crops will be negligible.
I assume the biggest risk being considered is product quality and not human occupational exposure. Therefore, lead concentrations in soil are generally low and pose little risk to product quality. I therefore consider the risks to agriculture as a result of the magnitude and concentrations of Pb in the soil presented in this report to be negligible.
