Herbicide toxicity awareness among smallholder farmers and agriculture extension officers in Malawi

Using evidence from field key informant and written questionnaire interviews with agriculture extension officers, focus group discussions with some smallholder farmers, analysis of packaging labels, and a detailed literature review, this paper argues that Malawian smallholder farmers handle herbicides without adequate information about the advantages and negative impacts of such herbicides because, it appears, the agriculture extension workers themselves lack requisite knowledge on herbicide toxicity. Further, the study finds that herbicides are marketed in Malawi in breach of Malawian law and in contravention of the Rotterdam Convention as the information on the herbicide labels is sometimes inadequate, misleading, and unavailable in local languages. This exposes farmers to potentially carcinogenic chemicals without their knowledge. The paper recommends, inter alia, that an awareness campaign about the long term harmful effects of herbicides be mounted countrywide and internationally to protect illiterate smallholder farmers from herbicide toxicity.

Herbicide Exposure and Toxicity to Aquatic Primary Producers

The aim of the present review was to give an overview of the current state of science concerning herbicide exposure and toxicity to aquatic primary producers. To this end we assessed the open literature, revealing the widespread presence of (mixtures of) herbicides, inevitably leading to the exposure of non-target primary producers. Yet, herbicide concentrations show strong temporal and spatial variations. Concerning herbicide toxicity, it was concluded that the most sensitive as well as the least sensitive species differed per herbicide and that the observed effect concentrations for some herbicides were rather independent from the exposure time. More extensive ecotoxicity testing is required, especially considering macrophytes and marine herbicide toxicity. Hence, it was concluded that the largest knowledge gap concerns the effects of sediment-associated herbicides on primary producers in the marine/estuarine environment. Generally, there is no actual risk of waterborne herbicides to aquatic primary producers. Still, median concentrations of atrazine and especially of diuron measured in China, the USA and Europe represented moderate risks for primary producers. Maximum concentrations due to misuse and accidents may even cause the exceedance of almost 60% of the effect concentrations plotted in SSDs. Using bioassays to determine the effect of contaminated water and sediment and to identify the herbicides of concern is a promising addition to chemical analysis, especially for the photosynthesis-inhibiting herbicides using photosynthesis as endpoint in the bioassays. This review concluded that to come to a reliable herbicide hazard and risk assessment, an extensive catch-up must be made concerning macrophytes, the marine environment and especially sediment as overlooked and understudied environmental compartments.