Peter van Straaten

Human exposure to mercury due to small scale gold mining in northern Tanzania.

In northern Tanzania large numbers of small scale miners use mercury in the gold extraction process causing contamination of the environment and risks to human health. Human exposure to Hg was assessed in populations in and around small scale gold mining camps by means of human hair and urine surveys. We also determined Hg concentration in fish in aquatic bodies close to these camps. Urinary Hg testing in three communities showed that 36% of the gold miners working with amalgam exceeded the WHO guideline concentration of 50 m gH grg creatinine. Data from a hair survey of fishermen and farmers confirm that at present, the fish-eating population close to the southern tip of Lake Victoria is at low risk with regard to Hg exposure. Concentrations in fish were low and ) 90% of the hair samples from the fish-eating population were below 2 mgrg T-Hg. Highest Hg concentrations in fish caught along the southern shores of Lake Victoria and in rivers draining from gold processing sites were . detected in lungfish species Protopterus aethiopicus , and lowest Hg concentrations in tilapia Oreochromis niloticus . and Tilapia zilii . Q 2000 Elsevier Science B.V. All rights reserved.

Potential of East African phosphate rock deposits in integrated nutrient management strategies

Phosphorus deficiency affects around 80% of the acid soils of western Kenya, but fertilizer use is limited due to high prices. This paper explores the potential of local phosphate rocks (PR) as a remedy within the context on an integrated soil fertility management approach. A promising phosphate rock is Minjingu PR (MPR, Tanzania), a sedimentary/biogenic deposit which contains about 13% total P and 3% neutral ammonium citrate (NAC) soluble P. On-farm trials in P-deficient soils in western Kenya demonstrate MPR to be as effective as triple superphosphate (TSP, 20% P) at equal P rates. The benefits are most pronounced with the integration of agroforestry technologies that improve soil fertility. Besides Minjingu PR, Busumbu PR from Uganda (BPR) is potentially another source of P. It is typical of the abundant but unreactive igneous PRs in eastern, central and southern Africa. Agronomic performance of BPR is poorer, though its lower cost and location near to P-deficient areas in western Kenya make it attractive in some situations. The policy implications of these findings are discussed further in the paper.

Solubility of apatite in clay and zeolite bearing systems: Application to agriculture

Abstract The various forms of apatite release Ca+2 and P-bearing anions into solution. The generally low solubility of these phases, however, has been a drawback to the use of apatite as a direct source of nutrient P in agriculture. Apatite has for the most part been used as a raw material for the production of the more soluble phases used in conventional fertilizers. This necessitates industrial processing by such techniques as acidulation or heat treatment, processes that inevitably increase the cost of the finished product. An alternative is to introduce a cation exchanger which will take up Ca+2, inducing further breakdown of apatite to produce a high enough concentration of P-bearing anions in solution to sustain a crop. Here, we demonstrate that framework, 2:1 sheet, and fibrous sheet silicates (zeolite, vermiculite and palygorskite) when added to apatite-H2O systems, work in this way.

Mining and Concentration: What Mining to What Costs and Benefits?

This chapter presents the activities in the Mining Node of Global TraPs, a multi-stakeholder project on the sustainable management of the global P cycle. The scope of the Mining Node is the extraction, primary processing of ore to produce phosphate rock concentrates and transportation to a port or processing plant. Phosphate ore deposits are primarily sedimentary in origin, although igneous, and, to a much lesser extent, guano deposits are also mined. A range of mining methods is used, and a significant amount of mining is by opencast or strip mining methods. Following the extraction of the ore, it undergoes a process of concentration before being transported to a plant for further processing or a port for export. World phosphate rock concentrates are produced in 37 countries, with the top ten accounting for 90 % of world production. Global phosphate production has increased to a 2011 level of 195 million metric tons and is set to increase still further to meet, primarily, the growing demand for fertilizers for food, feed, and biofuel production. The overarching objective of the Mining Node, aligned to that of the Global TraPs project, is to address the question: How can we contribute to sustainability in the phosphorus mining sector through promoting resource efficiency and innovation to avoid and mitigate negative environmental and social impacts, and contribute to food security? Based on this question, areas of focus for further research and case studies include (1) the optimization of mining and beneficiation recovery rates; (2) addressing environmental and social impacts; (3) small-scale phosphate mining; and (4) mining costs. Transdisciplinary projects teams, involving both science and practice, will work on these focus areas.