She was speaking after attending a hearing in Parliament on the possible fall out of Brexit on the environment.
The public hearing on “The impact of the UK's withdrawal from the EU on the environment, public health and food safety” was organised by Parliament’s environment, public health and food safety committee.
EPP group deputy McGuinness later told this website the consequences of Brexit could be felt “particularly on the island of Ireland.”
The reason, she said, is that there are ongoing concerns about the return of a hard border with controls and divergence between EU standards and UK standards post-Brexit.
She said there had been calls for Ireland to be treated as a single environmental area post-Brexit and for the existing levels of environmental protection to continue.
“When it comes to air quality, water and habitat protection, there are no borders,” said the MEP.
“The value of EU membership in ensuring cross-border, pan-European protections through environmental directives and regulations is in the spotlight.
“Achieving that important level of coordination post-Brexit should standards diverge will be difficult.”
In addition, there are competing claims between Ireland and the UK over the ownership of the waters of Carlingford Lough and Lough Foyle, two lakes along the border.
“This issue had receded in importance because of EU membership and common environment legislation. In addition, north-south cooperation under the Good Friday agreement also worked to ease differences.
“Access to healthcare and medicines could also be affected by a hard Brexit, which would impact badly on patients in Northern Ireland and the Republic of Ireland.”
She went on, “Common good safety standards protect citizens and here, again, there may be problems if the UK abandons the well-established food safety legislation in favour of a different regime.
“Animal health is an all-island concern and must remain so post-Brexit, but the mechanism to achieve that ambition has yet to be created.”
The deputy said, “Our combined actions on environment, health and food safety cannot be rolled back on because of Brexit, but there is no certainty that it will continue.
“There is a lot of work to be done by the UK to show how its ambition to leave the customs union and single market will not have negative consequences for these key issues.”
Other speakers at the workshop included Paul Laffin, of the British Medical Association, Virginia Acha, of the European Federation of Pharmaceutical Industries and Sue Davies of Which?
Meanwhile, the UK government has been accused of “sleepwalking” into a post-Brexit future of “insecure, unsafe and increasingly expensive food supplies, and has little idea how it will replace decades of EU regulation on the issue.”
A report by academics says UK ministers and the public have become complacent after decades of consistent food supplies and stable prices for the UK, something greatly helped by the EU.
Written by food policy experts from three universities, the report argues that there has been an almost complete lack of action so far in a host of areas connected to food and farming, including subsidies, migrant farm labour and safety standards.
“With the Brexit deadline in 20 months, this is a serious policy failure on an unprecedented scale,” said Tim Lang, professor of food policy at City University and one of the authors.
Erik Millstone from Sussex University, who compiled the study with Lang and Terry Marsden from Cardiff University, said the lack of government action was "baffling."
“We are surprised at the failure of the government to address a huge set of issues related to food and agriculture,” he said.
“They give the impression of sort of sleepwalking into this.”
The 88-page report notes that large elements of EU agricultural and fisheries policies would need major reform even if Britain remained a member. It warns that departure from the EU raises such urgent complications for food and agriculture that without focus on the issue “the risk is that food security in the UK will be seriously undermined”, leading to dwindling supplies and erratic prices.
It adds, “There are also serious risks that standards of food safety will decline if the UK ceases to adopt EU safety rules, and instead accepts free-trade agreements with countries with significantly weaker standards.”