1995 residue
results
Between July and December 1995 unexpectedly high
levels of the organochlorine lindane were found in retail milk samples. During
this period nine samples out of 216 exceeded the legally binding maximum residue
level (MRL) of 0.008 mg/kg (parts per million). Several other samples were at
levels approaching the MRL1. MRLs indicate whether good agricultural practice
has occurred and do not necessarily relate to health risks. In this case, health
limits have not been exceeded, according to scientists at the Pesticides Safety
Directorate (PSD), an executive agency of MAFF. Even at the highest levels
found, the lindane residues would not exceed the acceptable daily intake (ADI).
An adult would need to consume 10 litres of milk daily at the highest residue
levels found, for the ADI to be breached. Levels started to decline from October
1995 and generally returned to background levels early in 1996.
Some lindane residues would be expected to transfer into
other milk products, especially those with high fat content such as cheese.
Tests carried out in 1996 confirmed this. Out of 56 samples of British cheese,
21 contained levels of lindane at or below the MRL. A further seven contained
residues above the MRL. These results are similar to those in milk and again the
ADI was not exceeded.
What’s
going on?
Officials at MAFF and PSD are at a loss to explain how
these elevated results occurred. In April they held a series of briefings to
keep interested parties up-to-date, and to help resolve the mystery. These
residue levels are among the highest ever recorded in UK dairy produce. It is
particularly surprising as usage has declined since the 1960s and 70s. Figures
for the UK between 1991-94 show average annual lindane use of 42,450 kg, mostly
as a seed treatment on oilseed rape, wheat, turnips and winter barley over a
sown area of 543,695 ha2.
| Lindane detected in retail samples of UK milk obtained in 19951 (216 samples, MRL=0.008) | |
| Detection (mg/kg) | No. samples |
| <0.0004 | 117 |
| 0.0004 – 0.0009 | 51 |
| 0.001 – 0.008 | 39 |
| 0.009 – 0.01 | 7 |
| 0.02 – 0.03 | 2 |
Many
theories—no answers
Various theories of what happened have been put
forward, but it seems unlikely that the cause will be established. The routine
use of lindane as a seed treatment has been ruled out by MAFF because of the
timing of application and application rates are 80g per ha. The contamination
may have been a result of pollution. At least two major incidents involving
lindane occurred last year: one in Yorkshire and the other in Somerton, Somerset
(see PN30 p3). However, there is no geographical pattern to the elevated levels
and the timing of the specific pollution incidents do not match. Milk samples
were purchased from retail outlets across Britain and the samples showing the
highest residues were found in different locations. Also, if non-point-source
pollution had occurred, residues should have been picked up in other animals and
produce, which was not the case.
Lindane is volatile and can be transported across national
boundaries, so the source of the contamination could have been overseas. Lindane
has for example, been found at low levels in the Danish environment, where the
chemical is no longer used. However, if continental Europe was the source,
again, other produce should have been affected.
Another possibility is contamination of imported cattle feed.
According to UKASTA (the agricultural supply trade association) there was no
change in the pattern of imported cattle feed, and enquiries with supply
companies suggested lindane contamination was unlikely. There may have been
contamination from lindane use as veterinary medicine. Another theory is that
the dry weather last year may have allowed for the concentration of background
levels of lindane—but again, why was this not measured elsewhere?
MAFF review
MAFF has produced an evaluation of lindane which was
drafted before the high levels of lindane in milk were revealed3. The Advisory
Committee on Pesticides (ACP) recommended to ministers that MAFF-approved
lindane products should continue, whilst adopting measures to minimise risks.
The review considered the risk to humans, animals and the environment in
agriculture. The ACP found that reproductive studies from animal experiments
show lindane to be fetotoxic in several species. In a mouse study there were a
small number of mice with development effects at much lower dose levels than
would be expected. In terms of endocrine disruption, there is some evidence that
the oral administration of lindane can inhibit the formation of progesterone in
female mice and increase the metabolism of testosterone in male rats. The
Committee on Carcino-genicity of Chemicals in Food, Consumer Products and the
Environment reviewed epidemiological data and concluded that there is no
clear evidence of an association between lindane and breast cancer.
The ACP recommended that steps be taken to reduce operator
exposure. Approval holders of lindane seed treatment products should be
encouraged to introduce a programme of stewardship involving growers and their
consultants. The aim of this programme would be to ensure that seed is treated
only where strictly necessary.
Conclusion/comment
It seems the source of lindane contamination of milk
and cheese will probably never be identified. Although lindane approvals remain
in place, MAFF is encouraging decreased use. Clearly the pesticide industry has
developed far more sophisticated pesticides since lindane came onto the market
in the 1950s. It would seem feasible to withdraw lindane from most uses as a
precautionary move. Where no current alternatives exist, research should be
encouraged to find more environmentally acceptable treatments. (DB)